1333
Glossary of Defining Terms
π Band
Equivalent of the valence band in an organic
semiconductive material
σ Bond
Bond formed along the internuclear axis, between the
nuclei of the atoms. In ethylene, a σ bond is formed by
the overlap of two carbon sp2 hybrid orbitals
π Bond
Chemical bond formed between the nuclei of atoms.
There are two bonding regions above and below
a nodal plane containing the nuclei. In ethylene, a
π-bond is formed by the overlap of p orbitals on the
carbon atoms
π ∗ Band
Equivalent of the conduction band in an organic
semiconductive material
A
Abbe Number
(νd ) a measure of the dispersion (wavelength
dependence) of the refractive index n of transparent
materials at visible wavelengths.
νd = (n d − 1)/(n F − n C ), where d = 587 nm,
F = 486 nm, and C = 656 nm. Typically νd takes
values of 80–20, which decreases with increasing n d
from 1.5 to 1.9
Absorption Coefficient
(α) The absorption coefficient represents the
logarithmic decrement of the incident light intensity
per unit length in the material
Acceptor
Impurity in a semiconductor or any other
electroluminescent device capable of inducing hole
conduction and accepting a valence-band electron to
produce an acceptor energy level
Acceptor Level
A level with energy E a that acquires electron captured
from the valence band to an orbit near the acceptor’s
atom
Acceptor Concentration
Number of acceptors cm−3 . It refers to the total
concentration Na and the concentration of ionized
acceptors Na−
Accumulation
The condition in which, for an MIS structure, the
applied voltage to the gate electrode VG results in an
increase in the density of majority carriers near the
surface of the underlying semiconductor. The applied
voltage is less than the flatband voltage, VG < VFB
ACRT
Accelerated crucible rotation technique: a means to
stir liquids in sealed ampoules, leading to
improvements in crystal properties
Active Material
The main functional component of the thick-film
paste, usually in the form of a finely divided powder
Active Matrix Addressing
The technique used to write and change images on
complex liquid-crystal displays. Each display consists
of thousands of picture elements (pixels) arranged as
a matrix of columns and rows. Each pixel has
a transistor switch [thin-film transistor (TFT)], which
has been deposited onto one plate of the liquid-crystal
display. A voltage is applied sequentially to the rows
of pixels, and selected pixels within each row are
switched on by data voltages on the columns. As the
next row in the sequence is activated, the elements of
the previous row are switched off from the data line by
the TFT, but hold their charge as an electrical capacitor
until the row is addressed next time in the sequence,
after a full frame time. Thus the image is built up line
by line, and individual pixels must hold their charge
for the period of the full frame-address time
Air Mass Number
This is often abbreviated to AM followed by a number
and characterizes the intensity and spectrum of light
(modified by absorption in the atmosphere). The AM
number is 0 for no air mass (i. e. for a satellite solar
array), 1 for the sun directly overhead and 1.5 for the
sun at 45◦ to the horizon
All-Optical Switch
Optical inputs are switched by other optical signals.
The switching is produced in many cases by
refractive-index changes. Comparing electronic
devices such as transistors, in which an electrical input
is controlled by an electrical current, we expect that
the all-optical switch can work faster, being free from
electrical noises. However, at present, in contrast to
the µm scale of a transistor, an all-optical switch may
have cm scales
Amorphous Metaloxides
Glassy alloys of a transition metal with oxygen,
typical examples being TiO2 , Ta2 O5 , Nb2 O5 , and
Y2 O3 . In bulk form, these materials are typically
polycrystalline or crystalline ceramics. However,
amorphous thin films can be deposited with relative
ease, and they have been widely used as high-index
layers in optical filter design and as dielectric layers in
the microelectronics industry
1334
Glossary of Defining Terms
Amorphous Network
Network consisting of atoms distributed randomly
with a short-range order, i. e., holding a regular
coordination of atoms
Amorphous Semiconductors
Semiconducting materials having a random network
without long-range order
Amorphous Silicon
Thin films of silicon with a structure that is
noncrystalline but which have the advantage of
a higher absorption coefficient compared to crystalline
silicon
Amphiphilic
An organic molecule possessing both polar
(hydrophilic) and nonpolar (hydrophobic) chemical
groups. The classic examples are fatty acids, which
consist of a nonpolar (−CH2 −) chain terminating in
a polar −COOH acid group
Amphoteric Dopants
Dopants that may serve both as acceptors and donors
Amphotericity
This occurs when an impurity can act either as an
acceptor or a donor. In GaAs, a Si atom can take up
a site on either sublattice and can act as a shallow
donor or shallow acceptor
Analytical Electron Microscopy
The application of transmission and/or scanning
electron microscopy for the purpose of structural
and/or chemical microanalysis
Anion
The electronegative atomic component in
a compound, e.g. As in GaAs, Se in ZnSe
Annealing
Low-temperature heat treatment, normally in the
presence of Hg, with the aim of adjusting the electrical
properties of materials. The process of heating and
slowly cooling semiconductor materials to reverse
lattice damage. As a metallurgical term annealing
describes the use of heat to reduce the internal energy
of a crystal. This energy may be mechanical (strain) or
may represent variations in concentration, which can
be reduced by diffusion, etc.
Antiferromagnetically Coupled Media (AFM)
See synthetic ferrimagnetic media (SFM)
Anti-site Defect
Occurs in semiconductor compounds and is an
anion (cation) replacing a cation (anion) on a regular
cation (anion) lattice site e.g. AsGa (GaAs ). The
anion AsGa (cation GaAs ) anti-site is expected to be
a donor (acceptor) in the III–Vs and similarly in
the II–VIs
Apparent Bandgap Narrowing
Definition of apparent bandgap seen in bipolar
transistors due to the combined effects of bandgap
narrowing due to heavy doping and the use of
Fermi–Dirac statistics
Areal Density
Number of bits per unit area stored on a recording
medium. In disk drives, it is the product of the
bits/unit length times the number of tracks per unit
length (usually inches and the areal density is
frequently quoted in Gbits/in2 )
Arrhenius Relation
A general expression connecting the value of
a parameter in a thermally activated process to the
absolute temperature T . So a diffusivity
D = D0 exp(−Q/kB T ) where D0 , Q and kB are the
pre-exponential factor, the activation energy for
diffusion and Boltzmann’s constant, respectively
Astigmatism
A defect in the performance of a lens arising from the
lens asymmetry about the optic axis, leading to loss of
sharpness of an image at focus
A-Swirl
A network of dislocations loops. The origin is
a stacking fault of Si interstitials. The size of the
dislocation loops can be many µm
Attenuated Total Reflection (ATR)
Technique to measure infrared absorption spectra of
thin films on a prism with enhanced sensitivity
utilizing multiple reflections of an infrared beam in the
prism
Auger Electron Spectroscopy (AES)
A method in which an electron spectrometer is used to
measure the energy distribution of Auger electrons
emitted from a surface
Auto-compensation
Often associated with amphotericity,
auto-compensation occurs when the incorporation of
electrically active impurities of one type leads to the
automatic incorporation of electrically active defects
of the opposite type. As an example, the doping of
melt-grown GaAs with donors always leads to
inadvertent incorporation of acceptors at about one
tenth of the donor concentration
B
Back End of Line (BEOL)
A term generally describing the final points in the IC
fabrication process line, such as the interconnection
and packaging fabrication steps. These process steps
generally require lower thermal budgets
Backscattered Electrons
Incident electrons that have interacted with atomic
nuclei and scattered backwards with comparable
incident energy. They may be used for sample imaging
with contrast dependent on the local averaged atomic
number
Baldereschi Concept
Mean-value k-points in the Brillouin zone are defined
such that the value that any given periodic function of
Glossary of Defining Terms
the wavevector assumes at these special k-points is an
excellent approximation to the average value of the
same function throughout the Brillouin zone
Band Offset
The valence- and conduction-band offsets describe the
corresponding band-edge discontinuities at intimate
and abrupt semiconductor–semiconductor interfaces
Band Alignment
Type I: electrons and holes are confined within the
same layer. Type II: electrons and holes are confined
in different (adjacent) layers
Band Filling
An effect that takes place when a semiconductor is
illuminated with light at a frequency within the
absorbing region. Upon absorption of the incident
photons, the electrons undergo a transition from an
occupied band (VB) to the empty band (CB), thereby
partially populating the empty band
Bandgap (BG), Band Gap or Energy Gap
The forbidden energy gap between the valence band,
normally filled with electrons, and the conduction
band, normally empty of electrons. The bandgap
energy measures the energy difference between the
top of the valence band and the bottom of the
conduction band. The optical BG is the photon energy
above which semiconductor absorbs energy of
incident EM radiation. It may be direct or indirect,
depending on type of electron transition from VB to
CB the radiation induces; in Si, the optical BG is
indirect with E g = 1.17 eV at 4.2 K
Bandgap Engineering
The science of tailoring the semiconductor band gap
to control the electrical and optical properties of the
material
Barrier Height
The barrier height of a Schottky contact is the energy
distance right at the metal–semiconductor interface
from the Fermi level to the majority-carrier band-edge,
i. e., the conduction-band maximum in n-type and the
valence-band maximum in p-type contacts
Beam Effective Pressure Ratio
In molecular beam epitaxy, this is the ratio between
the partial pressures of the various components of the
molecular source beams
BEEM (Ballistic-Electron-Emission Spectroscopy)
Technique
A method to determine the barrier heights of Schottky
contacts by tunnel injection of almost monoenergetic
electrons from a biased metal tip into
metal–semiconductor contacts that pass the metal
films as ballistic electrons and are collected by the
semiconductors, provided their energy is high enough
to overcome the interfacial barriers
Birefringent Crystals
Crystals such as calcite that are optically anisotropic,
which leads to an incident light beam becoming
separated into ordinary (o-) and extraordinary (e-)
waves with orthogonal polarizations; incident light
becomes doubly refracted because these two waves
experience different refractive indices n o and n e
BLIP
Abbreviation for background-limited performance,
which describes the best signal-to-noise performance
that can be achieved with a detector. In this condition
the only noise stems from the random arrival rate of
photons and is therefore at a theoretical minimum
Blocking Temperature
Temperature where the magnetic exchange coupling
between an antiferromagnet and a ferromagnet
vanishes
Boltzmann Equation (BE)
Generally an integro-differential equation that governs
the carriers’ distribution function. At equilibrium the
BE is automatically satisfied by a Fermi distribution.
The generalized BE is a version revised to include
quantum effects in the carrier’s scattering and
interaction with EM fields. Methods for the solution of
the BE include the relaxation time, variational,
displaced Maxwellian and Monte Carlo methods
Boule
There are many terms used for large crystals. These
include boule, ingot and crystal. The top of the crystal
is called the seed end, the first to solidify, etc. The
bottom is called the tail or tang end
Bragg’s Law
Can be summarized by the defining equation
λ = 2dhkl sin θ, which must be satisfied for
constructive interference to occur, corresponding to
maxima in the positions of diffracted intensity
Bravais Lattice
A repetitive arrangement of points in space such that
the environment of each point is identically similar to
that of every other point. 14 such arrangements are
used to describe crystal systems
Bremsstrahlung
Electromagnetic radiation produced by the rapid
deceleration of an electron in the vicinity of an atomic
nucleus
Bridgman Growth (Technique)
Technique developed in order to grow compounds
where one component is volatile at the growth
temperature. The growth is carried out by physically
withdrawing the melt from its furnace, while the melt
crystallizes on a seed. The volatile component is
replenished from a reservoir in a separate furnace. The
arrangement of the equipment can be horizontal or
vertical, the former offering the possibility of viewing
the top of the solid/liquid interface and giving visual
feedback of the growth process
Brillouin Zone (BZ)
A primitive cell in the reciprocal-space lattice, which
proves to be body-centered cubic (BCC) for Si. The
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1336
Glossary of Defining Terms
BZ provides the domain of wavevectors k, which
relate to the electron momentum in crystal p = ~k.
Broadband Sensitizer
Typically a species that is co-doped along with
rare-earth ions into a glass host to increase the
pumping efficiency or radiative efficiency of the
rare-earth ions. Various sensitizers have been
demonstrated, including silicon nanoclusters, silver
ions, and other rare-earth ions (such as in the
sensitization of erbium by ytterbium)
Brooks–Herring (BH) Formula
Celebrated equation for the carrier’s momentum
relaxation time due to scattering by ionized impurities
Bulk Modulus
Ratio of the compressive or tensile force applied to
a substance per unit surface area to the change in
volume of the substance per unit volume
C
C/V Technique (Capacitance–Voltage Technique)
The C/V technique is a method to determine barrier
heights of Schottky contacts from the variation of their
capacitance as a function of applied voltage
Calamitic
Denotes the rod-like shape of the molecules forming
the majority of liquid-crystal phases that, therefore,
are known as calamitic liquid crystals
Capacitance Equivalent Thickness (CET)
Theoretical thickness of SiO2 that would be required
to achieve the same capacitance density as an
alternative dielectric material. This is extracted
directly from, for example, the accumulation region of
a C–V curve and has no further correction
Capacitance–Voltage (C–V)
C–V measurements of a MOS capacitor can be used
to determine the oxide thickness and the amount of
electrically active defects (fixed charge, trapped
charge, mobile charge, and interface trapped charge)
and mobile contaminants in the oxide. It can also be
used to determine the oxide thickness and the profile
of dopants at the semiconductor surface. It is
a common characterization technique used in wafer
fabrication facilities
Carrier Mobility
Measure of the effect of applying an electric field to
charge carriers (electrons or holes). It is the additional
velocity acquired by the carriers (drift velocity)
divided by the electric field
Carrier Range
Determines how far an injected carrier moves per unit
field before becoming immobilized in a deep trap.
Sometimes, it is calculated as the product of the drift
mobility and lifetime
Carrier Concentration
Number of the current carriers per cm−3 . It can be
electron concentration n and/or holes concentration p.
The intrinsic carrier concentration (n i ) is n = p in
a perfect crystal semiconductor that has not been
doped (i. e., an intrinsic semiconductor). The value of
n i for Si is approximately to 1.08 × 1010 cm−3 at 300 K
Carrier Velocity, Microscopic
Gradient of specific band spectrum E s (k) with respect
to p
Cascaded Second-Order Materials
Materials that exhibit second-order nonlinear
properties that act as an effective third-order nonlinear
material
Cathodoluminescence
Luminescence stimulated by energetic electrons
Cation
Electropositive atomic component in a compound, e.g.
Ga in GaAs, Cd in CdS
Cd-Based Compound Semiconductor
Semiconductor that contains the element Cd
Centro-symmetric
A crystal structure in which a center of inversion
exists is called centro-symmetric. There are 32 crystal
classes, among which 11 are centro-symmetric
Cermets
Standard form of thick films requiring exposure to
a high-temperature firing cycle, typically in the range
700–1000 ◦ C
Chalcogenide Glasses
Glasses that are amorphous alloys containing S, Se,
and/or Te. Typical examples include Se, GeS2 , GeSe2 ,
As2 S3 , As2 Se3 , and As2 Te3 . By intermixing these and
other binary chalcogenide glasses, a wide variety of
multicomponent glasses can be formed. Further,
a wide range of nonstoichiometric compositions is
possible. Several compositions have become standard
industrial materials, including Ge33 As12 Se55 and
Ge28 Sb12 Se60 . The chalcogenide glasses are
characterized by narrow bandgaps and good
transparency in the mid- to far-infrared wavelength
range
Characteristic X-Ray
An X-ray photon generated by the transition of an
outer-shell electron to an inner-shell vacancy of an
atom, with energy characteristic of the element
Charge-Blocking Layer
A layer that is sometimes placed between the
conductive layer and the subsequently coated layer
(usually the charge-generation layer) to prevent
charge injection in the dark
Charge Carriers
Generally current-carrying (free) electrons and holes
in conduction and valence bands, respectively, and
electrons trapped by nearby impurity atoms
Charge Generation
Conversion of absorbed light into charges that are
injected into, and subsequently transported through,
Glossary of Defining Terms
the charge-transport layer of an organic
photoconductor
Charge-Generation Layer (CGL)
A layer in an organic photoconductor in which light is
absorbed and converted into electrically charged
species
Charge-Generation Material (CGM)
The light-absorbing material in the charge-generation
layer
Charge Pumping
Electrical technique used to determine the interface
state density in MOSFETs. In its simplest
implementation, voltage pulses of well-defined
properties of amplitude, rise and fall times and
period are applied to the gate terminal of a MOSFET
with the source and drain terminals grounded, and
the substrate current is measured as the base level of
the gate pulse is swept from below accumulation to
above threshold voltage. The resulting substrate
current is then used to extract the interface trap charge
density (cm−3 )
Charge Transport
involves electron hopping through a polymer matrix
containing charge-transport moieties (see MDP). The
charge carrier for hole transport is the radical cation
and that for electron transport is the radical anion of
the charge-transport moiety
Charge-Transport Layer (CTL)
The layer in an organic photoconductor through which
charges generated in the CGL are transported
Charge-Transport Material (CTM)
The charge-transport layer dopant that transports
charge injected from the charge-generation material
Chemical Annealing
A concept to explain crystal formation by the
assistance of chemical species such as atomic
hydrogen during film growth
Chemical Vapor Deposition (CVD)
Technique for the growth of thin solid films on
a crystalline substrate as the result of thermochemical
vapor-phase reactions. This reaction occurs above
a solid surface, e.g. a diamond single crystal, which
causes deposition onto that surface. In the CVD
technique the thin films are obtained under
equilibrium conditions. The gas-phase reaction is
activated by temperature in order to create
condensable species that lead to film growth. Different
CVD techniques have been developed (See:
Mercury-sensitized photo-CVD, Hot-wire CVD,
MOCVD, MPCVD, PECDV). All techniques used for
the production of diamond require a means of
activating gas-phase carbon-containing precursor
molecules, usually CH4 , diluted by hydrogen
Chiral Nematic
Liquid-crystal phase in which the director is twisted
into a helical arrangement; the phase is, therefore, not
superimposable on its mirror image and so exhibits
macroscopic chirality. The chirality of the phase
originates from that of the constituent molecules. The
chiral nematic is sometimes referred to as a cholesteric
phase
Chromatic Aberration
A blurring of resolution due to the differing focal
lengths of a lens when acting on electrons of differing
energy
Cleave and Stain
This is a rapid, though destructive, technique for
assessing semiconductor structures. Particular
chemical mixtures affect the surfaces of different
semiconductor types in different ways, giving rise to
effects that can be seen in a simple optical
microscope. The sample is first cleaved to produce
a clean surface, preferably at an angle that tends to
magnify the scale of the structure, and then stained
CMT
A narrow-bandgap II–VI semiconductor compound,
Hg1−x Cdx Te, which is still the preeminent infrared
(IR) material
Coefficient of Thermal Expansion (CTE)
Increase in the length of a macroscopic material for
a given temperature increase. The units of CTE are
1/◦ C
Coercive Field
The electric field required to reduce the polarization in
a ferroelectric material to zero in a fully saturated
ferroelectric hysteresis loop
Coercive Squareness Parameter (S ∗ )
The slope of the major hysteresis curve of
a ferromagnetic recording layer normalized to the
ratio of the remanent
magnetization
to the coercive
field S∗ = 1 − Mr /Hc dM/ dH(H = −Hc )
Coherence Length
ξ is the shortest distance within which a considerable
change of the Cooper-pair density is possible
Cohesive Energy
The energy required to dissociate the atoms of a solid
into isolated atomic constituents
Columnar Phase
A liquid-crystal phase in which the constituent
molecules, usually disc-like, are stacked into columns;
these are arranged parallel to each other in either
a hexagonal or rectangular array
Complementary Metal Oxide Semiconductor (CMOS)
An MOS device technology consisting of nMOS and
pMOS transistor pairs
Complex
A bound state between two or more adjacent, like or
unlike species, e.g. an anti-site and a lattice vacancy at
a nearest-neighbor site on the same sublattice such as
AsGa VGa
Compositional Uniformity
A critical parameter in all ternary alloy systems that
1337
1338
Glossary of Defining Terms
determines a material’s usefulness in device
applications
Compound Semiconductor
Semiconductor crystals composed of two or more
atomic elements from different groups of the periodic
chart
Compressive Strain
Type of strain obtained when a strained Si1−x Gex
layer is grown on a silicon substrate
Compton Scattering
Transfer of energy from a photon to an electron,
leading to the scattering of a longer-wavelength
photon
Concentration Quenching
the reduction in luminescence efficiency and
luminescence lifetime of a laser glass when the
rare-earth dopant concentration is high. Quenching is
due to interactions between closely spaced rare-earth
ions at high concentrations. These interactions create
new pathways, other than the desired radiative decay,
for the ions to relax to the ground state after they have
been raised to a desired lasing level by pump energy
Conduction Band (CB)
Band of energies allowed for electrons in
a semiconductor, which is empty in undoped
semiconductors. There are many CBs, separated by
band gaps. However, CB term usually refers to the
conduction band that has the lowest energies, or
closest to the valence band (VB). It is seperated from
the VB by a band gap
Conductive Layer
The layer on which the charge-generation layer and
charge-transport layer are coated. It is connected to
ground in the electrophotographic process
Conductivity Mass
Used for electron or hole conductivity (mobility)
calculation
Conductivity
Product of the number of electrons or holes per unit
volume, the electronic charge and the mobility of the
carrier σ = neµe,h
Configuration Coordinate Model
Model of interaction between electronic system of
a luminescent center and the vibrational system of the
surrounding atoms and ions
Converse Piezoelectric Effect
The generation of mechanical strain in a material in
response to an applied electric field, where the strain is
linearly proportional to the applied field
Conversion Efficiency
Ratio of incident photon energy and output electricity
energy
Cooper Pairs
Bound electron pairs formed of electrons with
opposite spins and momenta (in their ground state
with zero electric field)
COP
A crystal-originated particle (COP) is a small
aggregate or cluster of vacancies. Usually, it is
of octahedral shape with (111) facets, but in the case
of nitrogen doping, it can also adopt the form of
a platelet or a rod-like cluster. The usual size is
70–200 nm
Corona Discharge
When a high voltage of 5–10 kV is applied to
sharp edges or fine wires of metals, the gas such as
air surrounding the metal is ionized and discharged.
If the voltage is DC, ions having the same polarity
with the DC voltage move toward a grounded
electrode
Correlation Factor ( f )
The jumps of a diffusing particle are generally not
random but correlated, i. e. successive jumps are not
independent of each other; f (always ≤ 1) is the ratio
of the jump rate of correlated jumps to the jump rate if
the jumps were random
Cotterell Atmosphere
The stress field around a dislocation can be reduced
if defects congregate around them. This results in
defect atmospheres, called Cotterell atmospheres,
which are commonly observed even when the
dislocation itself would not provide an observable
signature. EL2 defects aggregate in this way in SI
substrate material
Coupled Granular Continuous (CGC) Recording
Media
In perpendicular recording media: a recording surface
consisting of two layers: the first being granular and
the second consisting of multilayers of typically cobalt
and palladium
Critical (Transition) Temperature
The Tc is a characteristic property of the
superconductor in question. At Tc the resistance drops
abruptly to an unmeasurably small value
Critical Field
Bc is the magnetic field sufficient to destroy the
superconducting state in a type I superconductor
Critical Fluctuations
Variations of the superconducting order parameter
1/2
ψ = n C exp(iϕ) (where n C is the Cooper-pair
density) around the thermal equilibrium values
Critical Thickness
Maximum thickness of a strained layer that can be
grown on a substrate before relaxation of the layer
occurs
Cryopanel
Liquid-nitrogen-cooled surface within the growth
chamber arranged to minimize contamination of the
wafer surface by impurities
Current In the Plane (CIP)
Magnetoresistive device with the sense current
flowing in the plane of the films
Glossary of Defining Terms
Current Perpendicular to the Plane (CPP)
Magnetoresistive device with the sense current
flowing perpendicular to the plane of the films
CZ Crystals
Crystals grown according to the so-called Czochralski
technique
Czochralski and Liquid-Encapsulated Czochralski
(LEC) growth
Czochralski growth pulls a crystal from the melt. The
seed is held in a holder vertically above the melt and
rotated. After partial immersion into the melt, it is
slowly withdrawn and the crystal forms on the seed.
The growth takes place because of the increased heat
loss from the crystal compared to the melt. Rotation of
the seed and growing crystal leads naturally to
a near-cylindrical crystal from which circular
substrates can be sawn. The GaAs melt must be
protected against As loss if this method is to be used.
Boric oxide (see liquid encapsulation) liquifies on the
surface of the melt and, to some extent, on the crystal
and acts as a barrier against As loss. The boric oxide
also insulates the melt from the crucible; reducing the
rates at which impurities from the crucible are
introduced into the melt and aiding withdrawal of the
exhausted melt from the crucible after Growth
D
Dangling Bonds (Broken Bonds)
Point-like defects that are produced by breaking
covalent bonds. The dangling bond may have an
unpaired electron, two paired electrons, or no
electrons. These dangling bonds were denoted as D0 ,
D− , and D+ by Mott, the superscript representing the
charge state
Dark Decay
Rate of decrease of the surface potential of a charged
organic photoconductor
Data Rate
Rate at which the digital data, recorded or read back in
a digital storage device, is transferred. Characterized
by Mbytes/s or MB/s, where a byte (B) is eight bits
Debye Length
A measure of the distance beyond which the electric
field due to a point charge (e.g. an ionized dopant
atom) is screened by the free carriers (electrons or
holes) and becomes increasingly negligible
Deep-Energy-Level Impurities
Doping impurities or other impurities whose energy
level lies toward the center of the bandgap
Deep-Level Transient Spectroscopy (DLTS)
DLTS is a useful technique for measuring
concentrations of deep levels in conducting
semiconductors. Deep levels within the depletion
layer of a pn junction are filled by putting the junction
into forward bias. On applying a reverse bias, these
levels are allowed to empty thermally. This produces
a change in junction capacitance consisting of a series
of exponentials. From the temperature spectra
generated for different time windows of the transient,
Arrhenius plots can be made to determine the energy
level (eV) and capture cross section (cm2 ) of the
defects
Defect Chemistry
Representation of interactions between defect species
and free carriers (dopant, impurity, native defect,
electrons and holes) in terms of chemical-style
equations from which the concentrations of the
various species concerned can be obtained
Deformation Potential
Effective electric potential describing interaction of
carriers with the lattice deformation irrespective of
what is the cause of the deformation. It describes the
phenomenology of the interaction between carriers
and phonons of deformation types
Deformation Potential Parameters
There are two and four such parameters for electrons
and holes in Si, respectively. For holes the parameter
set includes one describing interaction with anti-phase
deformation of atoms in the nonequivalent primitive
cell’s positions
Density of States
Widely abbreviated as DOS, the density of states is the
number of energy states per unit energy interval at the
energy E. It stands for the density distribution of
allowed electronic energies in a material and is widely
used with respect to this distribution across the
bandgap of disordered semiconductors
Density-of-States Mass
Used for electron or hole density-of-states
calculations
Depletion
The condition in which, for a MIS structure, the
applied voltage to the gate VG electrode results in
a reduction of majority carriers near the surface of the
underlying semiconductor. This region is referred to as
the depletion layer. Charge remaining in this
near-surface region is due to ionized dopants present
in the channel region. This condition occurs for
applied voltages between the flatband and threshold
voltages, i. e. VFB < VG < Vthr
Depth of Field
The distance along an optic axis that an object can be
moved without noticeably reducing the resolution
Depth of Focus
Maximum spacing between an imaging screen and
a photographic plate (or CCD) that allows a recorded
image to be retained in focus
Depth Profiling
Monitoring of signal intensity as a function of
a variable that can be related to distance normal to the
surface, cf. compositional depth profile. Note: the
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Glossary of Defining Terms
signal intensity is usually measured as a function of
sputtering time
Depth Resolution
Depth range over which a signal changes by
a specified quantity when reconstructing the profile of
an ideally sharp interface between two media or
a delta layer in one medium
Detection Efficiency
Percentage of radiation incident on a detector system
that is actually detected
Detective Quantum Efficiency (DQE)
The ratio of the square of the signal-to-noise ratio at
the output of the detector to that at the input. The
relative increase in image noise due to an imaging
system as a function of the spatial frequency, f , is
expressed quantitatively as DQE( f ), which represents
the signal-to-noise transfer efficiency for different
frequencies of information in an image
Detectivity
A signal-to-noise parameter, normalized to area and
bandwidth, often used for photoconductive detectors
or single-element photovoltaic detectors
Devitrification
The transition of a glassy material to its lower-energy
crystalline state. This process is usually driven by
thermal energy, such as if the material is held at some
characteristic temperature above its glass-transition
temperature. The difference between the crystallization temperature and the glass-transition temperature
for a particular glass is one measure of its stability
DFT (Density-Functional Theory)
DFT is a quantum-mechanical approach to many-body
electronic structure calculations of molecular and
condensed-matter systems. The many-electron
wave-function is written in terms of the electron
density. The major problem with DFT is that the exact
functionals for exchange and correlation are not
known. The widespread approximations are the
local-density approximation (LDA) and GW
approximation (GWA). The LDA assumes the
functionals for exchange and correlation to depend
only on the density at the coordinate where the
functional is evaluated. LDA DFT calculations
dramatically underestimate the gaps of sp3 -bonded
semiconductors and insulators. In the GW
approximation, the exchange and correlation is
expressed as the product of a single-particle
propagator G and a screened interaction W. GWA
DFT calculations yield the gaps of sp3 -bonded
semiconductors and insulators generally to within
a few tenths of an eV
Diamond Structure
A structure in which each atom lies at the center of
a tetrahedron surrounded by four nearest neighbors
located at the points of the tetrahedron. In such
a structure diffusion is isotropic
Dielectric Constant/Susceptibility (DC/DS)
Basic material optical tensor property that linearly
connects the electric displacement to the electric-field
vector inside the material. For Si it is scalar. At optical
frequency DC/DS is a complex quantity
Dielectric Materials
A class of materials that are insulators or
nonconductors where charge imparted to one part of
the material is not communicated to any other part
Diffraction
The process of scattering and reconstruction of
radiation in specific directions as a consequence of
interaction with a periodic structure, e.g. light
interacting with a grating, or X-rays interacting with
a crystal lattice
Diffusion Coefficient or Diffusivity
The macroscopic parameter that characterizes the
jump rate or jump frequency of a species at the atomic
level. It is normally obtained by matching
experimental profiles to solutions of the appropriate
diffusion equation, e.g. Fick’s second law. The
diffusion coefficient measurement techniques include
Haynes–Shockley, time-of-flight and
noise-measurement-based methods
Diffusion Length
Measure of the spatial extent of a diffusion region.
Typically the concentration of a diffusant can be
expected to fall by more than a factor of 103 over three
diffusion lengths
Digital Printing
Technologies in which the image is comprised of
a pattern of pixels. In electrophotographic digital
printing the electrostatic latent image is written on
a charged photoreceptor using a computer-controlled
laser or LED bar
Dipping
Liquid-phase epitaxy technique in which the
substrate is lowered into the melt in a vertical
orientation
Direct Piezoelectric Effect
The generation of an electric polarization change or
a charge separation in a material in response to an
applied stress, where the polarization change is
linearly proportional to the applied stress
Director
Symmetry axis for properties such as the refractive
index or dielectric tensor of a liquid-crystal phase; at
a molecular level it is commonly associated with the
preferred orientation of the unique axis of the
constituent molecules, either rod-like or disc-like
Discotic
Indicates the disc-like shape of the anisotropic
molecules that constitute a class of liquid-crystal
phases known as discotic liquid crystals
Disorder Model
Derived from Monte Carlo simulation studies, this
Glossary of Defining Terms
model describes electronic transport in random media
in terms of disorder-induced fluctuations of both
hopping site energy and relative orientation
Distribution Function
A function of p (impulse) and the carrier’s coordinate,
which obeys Boltzmann’s equation and presents
a semiclassical probability description of a carrier’s
statistics and dynamics. At equilibrium, it converts to
the Fermi function over the carrier’s energy, which in
turn reduces to a Maxwell–Boltzmann distribution for
lightly doped semiconductors
Donor
An impurity in a material that is capable of inducing
electrical conduction in that material by transferring
an electron to the conduction band. A donor’s level is
the energy E d of an electron in an orbit near the donor
atom. The donor concentration is the number of
donors cm−3 , referring to either the total concentration
Nd and the concentration of ionized donors Nd+
Dopant
An atom from a different group of the periodic table
from the host atom that substitutes for it. It can be
a donor, acceptor or amphoteric and is deliberately
incorporated to give n- or p-type conductivity
Doped Semiconductor
A semiconductor that contains donors and/or
acceptors. Lightly and moderately doped
semiconductors contain impurities with energy levels
that are well separated from the CB and VB. Heavily
doped semiconductors (n+ - or p+ -type) contain so
many dopants that their energy levels merge with CB
or/and VB, which leads to metallic conduction at low
temperatures. For n-Si, the critical donor concentration
of this, Mott’s insulator–metal transition, proves to be
about 3 × 1018 cm−3 . Fermi–Dirac statistics must be
used for carriers in n+ - or p+ -type semiconductor, but
in n+ - or p+ -Si full degeneracy of carriers is met only
well below room temperature
DRAM
Dynamic random-access memory
Drift Mobility
Velocity per unit of applied field imparted to a charge
carrier by the electric field. In the presence of carrier
traps it is reduced from the free-carrier velocity by
the fraction of time a carrier spends in the trapping
centers
Drude Formula
Phenomenological equation for the free-carrier
contribution to the dielectric constant/susceptibility. It
contains two parameters: the effective plasma
frequency and the relaxation time
Drum Photoreceptors
Devices where the layers are coated sequentially on
a metal drum substrate
Dual-Layer Organic Photoconductor
A photoconductor with an architecture where the
charge-generation and charge-transport functions are
carried out in separate layers (see charge-generation
layer and charge-transport layer, respectively)
Dynamic Coercivity
The change of coercivity of small ferromagnetic
particles with switching time under thermal
excitation
E
E Center
A kind of unpaired-electron dangling bond in oxide
glasses. In SiO2 , an Si atom that is bonded to three O
atoms may have one E center. The center, which may
be produced by radiation, gives ESR signals and
optical absorption at ~ω ≈ 6 eV
E Layer
Thin ferromagnetic cobalt alloy film added to one or
two sides of the Ru layer in a synthetic ferrimagnetic
media to increase the exchange coupling
Easy Axis
Direction in a ferromagnetic sample along which the
magnetization is oriented in the absence of an external
magnetic field. In thin films, the easy axis is the
direction in a substrate surface along which the
director tends to align; it is determined by the nature
of the surface treatment
Edge-Defined Film-Growth Technique
Shaped crystals, including tubes, sheets, etc., are
grown through a die placed on the melt surface
Effective Mass
Generally a set of parameters describing the dynamics
of the current carriers, which may deviate drastically
from the free-electron mass. For Si, it includes the
effective mass tensor of electron in the CB (m t , m t ,
m l ) and the masses of heavy (m 1 ), light (m 2 ) of spin
orbital split-off (m 3 ) holes in the VB. Generally, m 1,2
depend on the direction of hole’s momentum.
Different averages over this direction define masses
that enter the conductivity and the DOS
Einstein Relation
An equation connecting the mobility µ, (speed per
unit electric field) of a charged particle to its
diffusivity D. Specifically µ = qD/kT , where q is the
electric charge on the particle. This expression is only
valid for nondegenerate material
EL(2)
Electron level number 2. The deep levels in most
semiconductors were labeled according to their
observation during DLTS measurements. EL levels are
donors (they are neutral when they have their
electron). HL levels are acceptors (they are neutral
when they have their hole). EL2 is the most important
deep donor level (actually, a double donor) and is
either the As anti-site defect or contains the As
anti-site as a component
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Glossary of Defining Terms
Elastic Compliance Constant (C)
Defined from Hooke’s law by X = Ce, where X is the
stress and e is the strain. It has units of pressure
Elastic Deformation
Deformation of a body in which the applied stress is
small enough that the object retains its original
dimensions once the stress is released
Elastic Stiffness Constant (S)
Defined from Hooke’s law by e = SX, where e is the
strain and X is the stress. It has units of inverse
pressure
Elasticity
A property of liquid crystals that causes the directors
to be uniformly aligned parallel to each other.
Deviations from this uniform ground state require the
addition of elastic energy to the liquid crystal
Electrically Conductive Adhesives (ECA)
Composite materials consisting of a dielectric curable
polymer and metallic conductive particles. The
polymer is an adhesive material that chemically reacts
with metals and other polymers to form a bond. The
metallic particles in the ECA form a network in the
cured joint that form an electrical conduction path
Electro-absorption
Generic term for all effects of changing the absorption
coefficient upon applying strong electric field. For Si,
the dominant is the change of the free carriers’
absorption in IR
Electrochemical Potential
In semiconductors (see Fermi level)
Electron Affinity
The energy distance from the conduction-band
minimum to the vacuum level at the semiconductor
surface
Electron-Beam Lithography
Method for micro- and nanoscale fabrication where
a pattern on a polymeric layer (resist) is exposed to
electron irradiation
Electron
Elementary particle having a negative charge of
1.602 × 10−19 C and rest mass m 0 equal to
9.109 × 10−31 kg
Electron–Phonon Scattering
In Si, in addition to scattering by deformation
phonons, scattering may also occur with
short-wavelength (inter-valley) phonons
Electro-optic Effect
A change in refractive index upon application of
a strong electric field. This is linked to
electro-absorption through the Kramers–Kronig
relation. It manifests itself as a change in
birefringence in response to an applied electric field
Electrophotography
Printing technology in which charged marking
particles are developed on an organic photoreceptor
with an image pattern of surface charge, the
electrostatic latent image, and the subsequent transfer
of these particles to a receiver
Electroplating
Process used to deposit a material on a conducting
substrate in a chemical bath containing metal ions
using electrical current
Eley–Rideal Reaction
A surface-reaction scheme in which an arriving
chemical species react on the surface without any
surface diffusion process. It is considered the
counterpart of a Langmuir–Hinshelwood reaction
Ellipsometry
Method of defining the optical constants by measuring
the ratio of reflectance for s- and p-polarized radiation,
and the relative phase shift between the two, at large
incidence angles
Emission Device
An emission device creates photons from extra
electron–hole pairs through a process called radiative
recombination. The electron–hole pairs are often
created by forward-biasing a pn junction
Encapsulation
A dielectric polymer material that flows over and
covers the electronic components in a package to
provide mechanical and electrical protection to the
packaged devices
Energy Gap
see Bandgap
Energy-Band Spectrum
Dispersion relation E s (k) of allowed electron energy
to k within the Brillouin zone. As a function of small
deviation of k from the extrema points of E s (k) it
proves to be anisotropic parabolic for the conduction
band and non-parabolic for valence band, forming
ellipsoid valleys and warped spheres, respectively, in
the Brillouin zone
Epitaxial Layer (or Epilayer)
Thin crystalline layer on a single-crystal substrate
with orientation and lattice structure determined by
the substrate crystallography
Epitaxy
(Greek; arrange upon). This is the growth of one
crystal (the epitaxial layer) on the surface of another
(the substrate) and where the orientation of the grown
layer is the same as the substrate. If the layer is of the
same material as the substrate, the growth is
homoepitaxial. If the layer and substrate are different,
the growth is heteroepitaxial. Usually, epitaxy can
only be performed where there is close match between
the lattice constants, although it is possible for a layer
of quite different lattice constant to be grown if there
is a change in crystal orientation between the layer and
the substrate. The term epitaxy was introduced to
describe the importance of having parallelism between
two lattice planes with similar networks of closely
similar spacing
Glossary of Defining Terms
Equivalent Oxide Thickness (EOT, t eq )
The theoretical thickness of SiO2 that would be
required to achieve the same capacitance density as an
alternative dielectric material. This is often
determined by quantum-mechanical modeling of the
C–V curve for thin dielectric layers (where tunnelling
effects result in substantial “leakage” current) and/or
where poly-Si gate electrodes (resulting in depletion
effects) are present
Etch Pit Density (EPD)
This is the usual way in which substrate suppliers
quote dislocation densities. EPD is found by etching
the surface in molten alkalis, like KOH, and viewing
the resulting pitted surface under an optical
microscope. Each pit represents a single dislocation
ending at the surface
Ewald Sphere
Geometrical construction used to illustrate the
relationship between a diffraction pattern and the
reciprocal lattice of a diffracting crystal
Exchange Field (Hua )
Parameter characterizing the strength of the coupling
of a ferromagnetic to an antiferromagnetic film.
Measured in Oe or A/m
Exciton
An electron–hole pair, which behaves like a H atom,
with a binding energy of 10–100 meV and lifetime of
≈ 1 ns. The wave-function, in principle, extends over
the whole crystal
Exhaustion Concentration
N = |Nd Na | is the maximum attainable carrier
concentration in a doped semiconductor
F
Fermi Level or Fermi Energy
For a metal, the Fermi level is defined as that energy
below which its one-electron levels are occupied and
above which they are empty in the ground state, i. e.,
at zero temperature. In the context of semiconductors,
the term Fermi level is a synonym for their
electrochemical potential
Ferroelastic
A material that exhibits a phase transition from
a non-strained to a strained state, generating
a spontaneous strain at the transition, and in which the
spontaneous strain can be switched between two or
more stable states by the application of a stress
Ferroelectric Domains
Adjacent regions in a ferroelectric crystal that have
their spontaneous polarization vectors inclined to one
another
Ferroelectric Hysteresis
The loop that is produced when the polarization in
a ferroelectric material is plotted as a function of
applied electric field
Ferroelectric Relaxor
A ferroelectric that shows a broad peak in relative
permittivity at the paraelectric-to-ferroelectric phase
transition and in which the temperature of the peak is
strongly dependent upon measuring frequency
Ferroelectric
A polar dielectric in which the polarization can be
switched between two or more stable states by the
application of an electric field
Fick’s First Law of Diffusion
For diffusion parallel to the x-axis the diffusant flux
(atoms per unit area per second) is equal to −D∂c/∂x
where c is the diffusant concentration which defines
the diffusivity D
Fick’s Second Law of Diffusion
Based on the first law, this law gives the rate of build
up of the diffusant concentration at a given depth as
∂c/∂t = ∂(D∂c/∂x)/∂x
Field-Effect Transistor (FET)
A transistor where the current between two electrodes
(the drain and source) is modulated by the electric
field from a third electrode (the gate)
Field Emission
Electron emission from a metal or semiconductor
into vacuum under the influence of a strong electric
field
Figure-of-Merit (FOM)
Measure of the performance of an integrated circuit
technology. The time delay associated with signal
propagation is a common metric
Fill Factor (FF)
Measure of the maximum power that can be obtained
from a photovoltaic solar cell compared with the
product Isc · Voc
Firing
One of the key stages of the thick-film production
process. It is usually undertaken in a continuous-belt
furnace at temperatures of up to 1000 ◦ C
Flatband Voltage (V FB )
The voltage applied across an MIS device at which
there exists no charge in the semiconductor. As
a result, the valence and conduction band structure of
the semiconductor is flat. This condition occurs when
this voltage equals the workfunction difference
between the metal electrode and the semiconductor
under ideal conditions. The presence of charges in the
insulator or at the interface, due to defects, modifies
the voltage required to achieve the flatband condition
Flexoelectricity
Generation of a macroscopic electrical polarization in
a nematic liquid crystal when the director distribution
is deformed from its uniform state of alignment. The
inverse of this effect is the deformation of the director
distribution when an electric field is applied to
a nematic; the magnitude of the deformation is linear
in the field
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Glossary of Defining Terms
Flip Chip
Integrated-circuit-level interconnect that can be used
to replace wirebond interconnects. The flip chip is
a solder bump on an area array on the chip surface that
routes the power, ground and signals from the
integrated circuit to the bumps. The metallization on
the IC surface is called the under-bump metallurgy
that forms a metallurgical bond with the solder. The
flip-chip die is joined to the package by placing the die
face down on the matching bond pads on a substrate
and reflowing the solder to form an electrical, thermal
and mechanical interconnect
Floating Gate Current
Very small gate currents (≈ fA or less) can be
measured using the floating gate technique in which
the drain current of a MOS transistor is measured after
the gate bias has been removed. Then, by using the
decay in the drain current as a function of time and the
measured drain current versus gate voltage
characteristics and the oxide capacitance, the gate
current can be calculated
Floating Zone (FZ) Technique
This technique uses a solid feed rod that is melted at
its lower end by a high-frequency coil. The melt flows
through a central hole of the coil down to the growing
crystal below the coil. The FZ technique does not need
a crucible. Hence, the melt is not contaminated by
other materials. The crystals that are grown according
to the FZ technique are called FZ crystals
Fluence
This is the total, time-integrated, flux of particles
(electrons, protons, ions, etc.) that reach a unit area of
sample. It can be used to represent the total number of
ions implanted into a surface and is sometimes called
the dose
Fluorescence
Luminescence with a lifetime 10 ns
Fluoride Glasses
Multicomponent glasses, typically based on fluorides
of zirconium, barium, lead, gallium, lanthanum,
aluminum, and sodium. They have a wide
transparency range, from ultraviolet to mid-infrared
wavelengths. They also have low characteristic
phonon energies and can dissolve large concentrations
of rare-earth ions. For these reasons, they are
extremely popular as hosts for rare-earth-doped
amplifiers and lasers operating in the UV–visible and
mid-infrared regions
Flux Lines (Vortices)
Regions in which magnetic flux enters a type II
superconductor in the mixed state. Screening currents
flow around each of the flux lines. Due to the repulsive
vortex–vortex interactions a hexagonal flux line lattice
is formed
Flux Pinning
An effect caused by defects. The energy for the
formation of the normal cores of the flux lines is
reduced in regions with a reduced Cooper-pair density
Flying Height
Spacing between the bottom of the slider and the top
of the recording medium in a disk drive
Forced Convection
Process of forced flow of fluid
Fourier-Transform Infrared (FTIR) Spectrometry
A means of performing infrared absorption
measurements with great speed and precision, based
on an optical interferometer
Four-Point Probe
A popular technique used to measure the resistivity
(Ω cm) of a semiconductor sample. Four collinear
probes are equally spaced and a current is applied
through the outermost probes and the voltage
difference across the two inner probes is measured.
From the voltage and current values, the resistivity
can be calculated assuming that the contact and
spreading resistances between the probes and the
semiconductor and the resistance of the probes are
negligible in comparison to the resistance of the
semiconductor
Franck–Condon Principle
Absorption and emission of light takes place in so
short a time that the atomic coordinates in ground and
excited states are unchanged; i. e. transitions are
vertical on a configuration coordinate model
Free Convection
The process of movement of fluid through
a temperature gradient
Free Film
Ferromagnetic film in a magnetoresistive or spin-valve
read head in which the magnetization can respond
easily to an external magnetic field
Friedel’s Law
A law that states that the intensity of an hkl reflection
in a diffraction pattern is equal to the intensity in the
opposite hkl reflection
Front End Of Line (FEOL)
A term generally describing the initial points in the
integrated-circuit fabrication process line, such as the
transistor fabrication steps. These processes generally
require higher thermal budgets
G
Gate Oxide Integrity (GOI)
The GOI measures the breakdown stability of the
oxide layer of a MOS capacitor when a voltage is
applied to the capacitor. There are different types of
gate oxide integrity tests. Most of them are
standardized. This may currently be the best method
to detect the density of very small voids
Geminate Recombination
The primary recombination of a correlated
Glossary of Defining Terms
(quasi-bound) hole–electron pair immediately
following photoexcitation
Ghosting
The change of X-ray sensitivity of the X-ray image
detector as a result of previous exposure to radiation.
In the presence of ghosting, a shadow impression of
a previously acquired image is visible in subsequent
uniform exposures
Giant-Magnetoresistive (GMR) Effect
Change in the resistivity of a stack of ferromagnetic
films coupled by thin non-ferromagnetic films when
the orientation of the magnetization of the films
adjacent to the non-ferromagnetic film is varied. The
change in resistivity with low temperatures and high
magnetic fields was observed to be as large as 50%:
hence the adjective giant
Glass Ceramics
Glass that contains crystalline particles or regions.
Such materials may be transparent or smoggy
Glass Frit
Binding matrix within the thick film. This binds the
active particles together and also bonds the thick film
to the substrate
Glass-Transition Temperature
The approximate temperature at which a material
changes from a supercooled liquid to an amorphous
solid, or vice versa. The transition is marked by an
abrupt but continuous change in slope of the specific
volume and enthalpy versus temperature curves.
Viscosity varies rapidly near the glass-transition
temperature, which is also sometimes called the
softening temperature
Glow Discharge Spectrometry (GDS)
A method in which a spectrometer is used to
measure relevant intensities emitted from a glow
discharge generated at a surface. This is a general
term that encompasses glow discharge
optical-emission spectrometry (GDOES) and glow
discharge mass spectrometry (GDMS). GDOES is
a method in which an optical-emission spectrometer is
used to measure the wavelength and intensity of light
emitted from a glow discharge generated at a surface.
GDMS is a method in which a mass spectrometer is
used to measure the mass-to-charge quotient and
abundance of ions from a glow discharge generated at
a surface
Gradient Freeze Growth
This technique is similar to the Bridgman method
except that the melt is not physically removed from
the furnace. Instead, the temperature gradient along
the melt is controlled electrically so that solidification
commences at the seed and progresses until the melt is
exhausted. Once again, both horizontal and vertical
arrangements are possible and often the reservoir is
replaced by liquid encapsulation to impede As loss
from the melt. This is now the favored technique for
the growth of most GaAs substrate material
Grading
Grading is the gradual change from one semiconductor
to another, exemplified by the gradual change from
GaAs to GaAsP that is necessary in some LEDs
Gratzel Cell
Named after its inventor, Michael Gratzel, this is
a dye-sensitized cell using a porous TiO2 substrate to
collect the photo-generated charge
GRINSCH Laser
A graded-refractive-index separate-confinement
heterojunction laser (see SCH Laser). Optical
confinement is optimized by grading the composition
of the cladding layers
Gunn Diode
(See negative differential resistance). This is a device
based on low-doped n-type GaAs and relies on the
NDR effect. It is used for the generation of low-power
microwave currents
H
Hall Effect
The deflection of a charged particle moving in
a magnetic field that is perpendicular to its motion.
The deflection is due to the Lorentz force on the
charged particle and it causes the charges to
accumulate in one side of the sample. The voltage
measured at right angles to the current flow is called
the Hall voltage. The Hall effect can be used to
characterize the mobility (cm2 /Vs), resistivity (Ω cm),
type of carrier and carrier density (cm−3 ) of
a semiconductor sample. The Hall mobility is the
product of conductivity and the Hall constant (the
transverse-electric-field Hall field divided by the
product of the current density and the magnetic
induction) for a conductor or semiconductor;
a measure of the mobility of the electrons or holes in
a semiconductor. The Hall coefficient and factor relate
µH linearly to σ and µ, respectively
Hard Axis
Direction in a ferromagnetic sample at right angles to
the easy axis
Hard Magnetic Bias Film (also Longitudinal Bias Film)
Permanent magnetic film abutted to the free film in
a magnetoresistive or spin-valve head to eliminate
magnetic domains
Head Field Slope Parameter (Q)
The maximum slope of the magnetic field of a write
head in the direction of the magnetization of the
recording layer normalized to the coercive field (Hc )
x / dx
divided by the magnetic spacing (d), Q = dH
Hc /d
Heat Capacity
The amount of heat required to change the
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Glossary of Defining Terms
temperature of a substance temperature by one degree,
with units of energy per degree
Heteroepitaxy
The growth of a layer of markedly different
composition from the substrate, i. e. the epitaxial layer
and the substrate are made from different materials,
e.g. the diamond growth on an iridium single-crystal
substrate. Another example is the growth of
Gax In1−x P y As1−y layers lattice-matched to InP. The
heteroepitaxial growth techniques are chemical-vapor
deposition, liquid-phase epitaxy, and molecular-beam
epitaxy
Heterojunction Bipolar Transistor (HBT)
A modification to the standard bipolar transistor where
a heterojunction is used to control the carrier flow at
the base
Heterojunctions and Heterostructures
A heterojunction is the junction between different
materials (e.g. GaAs and AlGaAs with different
bandgaps). Such a junction exhibits several properties
that may be very useful to device manufacturers.
These include changes in the energies of the valence
or conduction bands, or both, and changes in the
optical properties. A heterostructure is
a semiconductor structure where the properties of
heterojunctions are exploited
Heterojunction Laser
A semiconductor laser where both electrical and
optical confinement exploit the properties of
heterojunctions is a heterojunction laser. If the active
region is sandwiched between two heterojunctions, the
laser is termed a double heterojunction
Hexagonal As
The natural form of elemental arsenic
HgMnTe
An alternative Hg-based ternary system to CMT
High-Electron-Mobility Transistor (HEMT)
This is a modification of the metal semiconductor
field-effect transistor (MESFET) where the separation
of the electrons in the channel from the ionized donors
is achieved by using a heterojunction. This results in
higher electron mobility, and thus greater speed and
lower noise
High Index Contrast
Waveguides or devices fabricated using two or more
materials that have very different refractive index.
High index contrast is the basis for the confinement of
light to very small cross-sectional-area waveguides or
very-small-volume optical cavities, either using total
internal reflection or photonic bandgap effects. High
index contrast is thus the basis for increased density of
optical integrated circuits
High-Temperature Solution Growth
Slow cooling, or top-seeded (similar to Czochralski)
growth of materials in a solution designed to reduce
the freezing point of the desired phase below a critical
temperature
Homeotropic Alignment
Alignment of the director perpendicular to the surface
of a substrate
HOMO – Highest Occupied Molecular Orbital
The highest energy molecular orbital of an atom or
molecule that contains an electron. If the atom or
molecule were to lose an electron, it would most likely
lose it from this orbital
Homoepitaxy
Epitaxial growth of a layer of the same composition as
the substrate
Homojunction
Junction between materials of the same chemical type
but of different electrical properties. For example,
a p–n junction in GaAs is a homojunction
Hopping Conduction
Electronic transport that localized electrons hop from
site to site with the assistance of phonons
Hot-Carrier Phenomena
Group of effects associated with the carrier transport
in high electric fields. For Si, it includes the nonlinear
relation between drift velocity and electric field with
saturation (n-Si) and near to saturation (p-Si),
anisotropy of drift velocity regarding the electric
orientation relative to the crystallographic axes (the
Sasaki–Shibuya effect) and the diffusion’s anisotropy
as regards the density gradients along and
perpendicular to the strong electric field
Hot-Wire Chemical Vapor Deposition (CVD)
The same technique as catalytic CVD, which is used
for thin-film growth through decomposition of source
gas materials utilizing catalytic reaction on the heated
filament
Huygens’s Principle
Concept used to explain the propagation of
a wave (and diffraction processes), in that every
point on a primary wavefront acts as a source of
spherical wavelets, the envelope function of which
acts to reconstruct the primary wavefront a short time
later
Hybrid Circuits
Circuits consisting of electronic elements made from
differing enabling technologies such as thick-film,
thin-film, monolithic silicon, etc.
Hybridization
In molecules, the orbitals occupied by the electrons
are seldom pure s or pure p orbitals. Instead they are
mixed or hybrids, formed by combining the s and p
orbitals. Examples are sp (linear), sp2 (trigonal and
planar) and sp3 (tetragonal)
Hydrothermal Growth
Growth that takes place in aqueous-based solutions at
high temperatures and high pressures
Glossary of Defining Terms
Hysteresis
The state of the magnetization in response to an
external magnetic field depends on the initial state of
the magnetization
I
I/V Technique (Current–Voltage Technique)
The I /V technique is a method to determine barrier
heights and ideality factors of Schottky contacts from
their current–voltage characteristics
IDCA
Abbreviation for for integrated detector cooler
assembly, a commonly used infrared detector scheme
in which the detector is mounted directly on the cold
finger of a cryocooler (often based on Stirling cycle
engines). The detector and cold finger are then
enclosed in a vacuum vessel with a transparent
window and optical baffles
Ideality Factor
The ideality factor of Schottky contacts characterizes
the variation of their barrier heights as a function of
applied voltage
Image Lag
Lag is the carryover of image charge generated by
previous X-ray exposures into subsequent image
frames. The residual signal fractions following
a pulsed X-ray irradiation are referred to as image lag
Impact Ionization
Process of generation of electron–hole pairs by
carriers moving in an electric field higher than the
breakdown threshold, which for Si is of the order of
3 × 105 V/cm
Improper (or Extrinsic) Ferroelectric
A ferroelectric material in which the spontaneous
polarization is not the primary order parameter.
Frequently, the primary order parameter is the
spontaneous strain associated with a ferroelastic phase
transition
Impurity
A foreign atom unintentionally present in the
semiconductor, incorporated either during growth or
processing
In Situ Monitoring
Tools to help in understanding layer growth kinetics
and to provide monitors suitable for feedback control
in epitaxial growth systems
Inelastic Scattering
The result of a collision between a photon or electron
and the nuclei or electrons of a material, such that
there is a net change in the internal energies of the
system and in the sum of the kinetic energies before
and after the collision
Infrared-Laser-Absorption Spectroscopy (IRLAS)
Technique to determine density of gas-phase
molecules and chemical species using infrared
absorption spectra
Infrared-Reflection-Absorption Spectroscopy (IRRAS)
Technique to determine the surface-bonding
configuration on the film-growing surface using light
absorption during reflection of infrared beam
Integrated Circuit (IC)
Combination of active and passive circuit elements to
enable computational logic or analog operations
Integrated Optics/Photonics
The manufacture of photonic elements and circuits on
a planar substrate, typically using thin-film deposition,
lithography, and etching steps. Typically, the substrate
is a glass or semiconductor wafer and the photonic
elements are guided-wave devices
Interconnect
The system of metal conducting lines and contacts
among IC components. The categories include local
(between neighboring devices), intermediate (between
neighboring circuit elements), and global (across the
IC chip)
Interdiffused Multilayer Process (IMP)
The process of obtaining a uniform alloy composition
of Cdx Hg1−x Te by the growth of alternate layers of
the binary compounds that are thin enough to
completely interdiffuse within the time of growth
Interface Trap Density
The density (cm−3 ) of positive or negative charges
located at the silicon/silicon dioxide interface, due to
defects induced by oxidation, structural defects,
impurities or other defects caused by bond-breaking
mechanisms such as radiation or hot carriers. These
states are typically in electrical communication with
the charges in the channel of a MOSFET and results in
stretch-out of the capacitance–voltage characteristics.
They also affect the turn-on and turn-off
characteristics of a MOS transistor
Interface-Induced Gap States
Because of the quantum-mechanical tunnel effect, the
wave-functions of electrons tail across semiconductor
interfaces in energy regions where occupied states
overlap a bandgap. These evanescent waves are the
continuum of the intrinsic interface-induced gap states
Intergrain j c
Macroscopic transport critical current density, which
can be much smaller than the intragrain jc because of
the weak-link behavior of large-angle grain
boundaries in the cuprate superconductors
Intermetallic Compounds
Substances that form between pad metallizations and
the active components of molten solder (typically Sn).
For Cu metallization, the Sn reacts to form Cu3 Sn
and Cu6 Sn5 intermetallics. For Ni, the Sn reacts to
form Ni3 Sn4 . These intermetallics typically form at
the interface of the solder and the metallization and
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1348
Glossary of Defining Terms
are usually more brittle that the solder or the
metallization
Intermetallic Reactions And Phases
Two or more metals can react chemically to produce
compounds. These are revealed in phase diagrams as
labeled, vertical lines. The compound is often referred
to as an intermetallic phase
Interstitial
A site lying between regular lattice sites that can be
occupied by dopant, impurity or host atoms. The latter
case is known as a self-interstitial. They generally
behave as a donor
Inter-subband (ISB) Transition
Transition between confined states within the
conduction or valence bands
Intragrain j c
is the value of jc within a single grain, limited only by
the pinning properties
Intrinsic Point Defect
Is the general term for either a vacancy or a Si
interstitial in the Si matrix
Inversion
Condition in which, for a MIS structure, the applied
voltage to the gate electrode VG results in an increase
of minority carriers near the surface of the underlying
semiconductor. This region is referred to as an
inversion layer. When present in a MISFET, this
condition results in a conducting channel between the
source and drain regions. This condition occurs for
applied voltages beyond the threshold voltage, i. e.
Vth < VG
Inversion Symmetry
A system in which the laws of physics are unchanged
by the operation of inversion
Ion Implantation
This is a method of introducing impurities into the
surface of a solid. The impurity atoms to be introduced
are ionized and accelerated by a high voltage, up to
106 V in some instances. They penetrate the surface to
a depth dependent on their energy. Unfortunately, this
disrupts the crystal lattice by introducing irradiation
damage and this must be repaired by annealing at
elevated temperatures before the electrical activity of
the implanted atoms can be obtained
Ionization
Process of forming an electrically charged atom (ion)
Ionization Energy
The energy distance from the valence-band maximum
to the vacuum level at the semiconductor surfaces
IPEYS technique (Internal Photoemission Yield
Spectroscopy)
IPEYS is a method to determine barrier heights of
Schottky contacts and band offsets of semiconductor
heterostructures by photoinjection of hot electrons
over the energy barriers at metal/semiconductor and
semiconductor/semiconductor interfaces, respectively,
as a function of the photon energy of the exciting light
Irreversibility Line
Situated well below the upper critical field, this line
separates a region without pinning and zero jc , above
the irreversibility field, from a region with pinned
vortices ( jc > 0)
Irvin Curve
The experimental resistivity ρ of Si at room
temperature versus N, the free-carrier concentration
K
Kikuchi Lines
Diffuse background of lines in a diffraction pattern
formed by the elastic scattering of incoherently
scattered electrons
Knudsen Cell
High-vacuum oven from which molecular beams can
be produced in molecular-beam epitaxy. These ovens
are usually fitted with temperature sensors. Shutters
mounted in front allow the beams to be turned on and
off, as required
Kramers–Kronig Relations (KKR)
Dual integral relations between the real and imaginary
parts of one-sided Fourier transform of causal
functions of time, which includes all physical
admittances. The KKR allow us to define the optical
constants based on KKR relations for amplitude and
phase of complex reflection coefficient from opaque
sample of material under measurement
Kyropoulos Technique
This is similar to the Czochralski method but the
extent of pulling is limited, producing crystals of
greater diameter but shorter length
L
Langmuir–Blodgett Film Deposition
Method to build up multilayer structures of organic
materials by the transfer of a monolayer floating on
a water surface to a solid substrate as the latter is raised
and lowered through the monolayer/water interface.
Deposition modes include Y-type (monolayer transfer
from the water surface to the substrate on both the
upward and downward motion of the latter through the
monolayer/air interface), X-type (film transfer only on
downward motion of the substrate) and Z-type (film
transfer only on the upstroke)
Laporte’s Rule
Transitions between states of the same parity are
forbidden
Laser Crystallization
A useful method to fabricate polycrystalline
semiconductor showing high electron mobility by
Glossary of Defining Terms
irradiating laser beam on amorphous semiconductor
thin films
Laser-Induced Fluorescence (LIF)
Technique to determine the density of gas-phase
atoms and molecules whose optically excited states
are emissive states
Lattice-Matching
Growth of quantum wells on a substrate with the
same, or very similar, lattice constant
Law of Mass Action
An equation linking the concentrations of the various
reacting species in a chemical-type equation, derived
from defect chemistry analysis
Lifetime
Minority-carrier lifetime is one of the electrical
parameters that determines the performance of IR
devices; it can be affected by impurities and/or
dopants
Light-Induced Defect Creation
The defect creation associated with illumination of
samples. This is normally observed in amorphous
materials having a flexible network
Lineage
A reduction in total dislocation strain energy can be
obtained either by polygonization or by dislocations
arranging themselves in linear arrays. The latter
results in the creation of a small-angle grain boundary
or lineage. The reader will find examples of this in
most books on materials science
Liquid Crystal
State of matter with properties characteristic of both
a liquid and a crystal; that is, it flows like a liquid and
certain properties are anisotropic like those of
a crystal. At the molecular level the phase has
long-range orientational order and some element of
translational disorder at long range
Liquid-Encapsulated Czochralski Technique
An inert layer, usually B2 O3 , is used, which floats on
the top of the melt to prevent loss of volatile
components; this is used for As- and P-containing
compounds
Liquid-Phase Epitaxy (LPE)
LPE is epitaxial growth of a layer by dissolving the
required material in a liquid. On cooling, the material
becomes supersaturated and forms a solid film. If this
film is deposited on a substrate the growth can be
epitaxial
Localized Vibrational Mode (LVM) Absorption
Form of mid- to far-infrared absorption resulting from
simple vibrations of light atoms in a heavier lattice.
Such vibrations do not couple well to lattice vibrations
and result in sharp absorption lines whose frequencies
are directly related to mass and whose strengths are
proportional to concentration. LVM absorption is
particularly suited for measuring carbon
concentrations in SI GaAs
Longitudinal Magnetic Recording
Recording system consisting of write and read head
and a recording media where the magnetization is
parallel to the surface of the recording medium
Long-Range Disorder
Defined by the absence of the long-range order, i. e.the
lack of periodic arrangements of atoms
Low-Dimensional Structure
Heterostructure with dimensions comparable to the
wavelength of an electron or hole, typically less than
100 Å, so that quantum effects are important
Low-Frequency Noise
Electrical measurement of the current or voltage noise
spectral densities of a semiconductor component,
typically at frequencies from ≈ 1 Hz to ≈ 100 kHz.
The units are in A2 /Hz for current noise spectral
density and V2 /Hz for voltage noise spectral density.
It is a sensitive electrical technique that can be used to
probe microscopic defects in semiconductor
components and as a gauge of their reliability
Low-Temperature Co-fired Ceramic (LTCC)
A composite material structure made of alumina
bonded at a temperature below the sintering
temperature of alumina using a glass binder. In
a substrate form, LTCC can be co-fired (melting the
glass and bonding the alumina while capturing the
metal interconnects and lines) at lower temperatures
so it is possible to use higher conductivity materials
like Cu or Ag conductors in the ceramic
Low-Temperature Solution Growth
Normally used for water-soluble materials, with
growth being progressed by either slow cooling or
solvent evaporation
LPE
Liquid-phase epitaxy is growth of a (normally) thin
epitaxial layer from the liquid phase onto a suitably
lattice-matched substrate by dipping, tipping or sliding
boat means
L-pit
see A-swirl
Luminescence
In general terms, is the emission of light by
a luminescent material (also called phosphor) due to
conversion of a certain type of energy into
electromagnetic radiation over and above thermal
radiation. The luminescence is the light emitted by
nonthermal sources in contrast with the emission of
radiation from a heated object, which is called
incandescence. In accordance with the source of
energy the luminescence may be the
photoluminescence (excited by external illumination),
electroluminescence (induced by the passage of
electrical current), cathodoluminescence (excited by
irradiation with electrons), triboluminescence (excited
by mechanical treatment, e.g. grinding),
chemiluminescence (emitted during chemical
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Glossary of Defining Terms
reaction), bioluminescence (appearing as a result of
biological processes), thermoluminescence (cased by
the rise of temperature) and so on
LUMO – Lowest Unoccupied Molecular Orbital
Refers to the lowest-energy molecular orbital of an
atom or molecule that does not contain an electron. If
the atom or molecule were to accept an electron, it
would be most likely to do it with this orbital
LW
Abbreviation for long wave, this term refers to the
transparent atmospheric window between the
wavelengths 7.5 µm and 14 µm (sometimes called the
thermal band). The edges of this window are
influenced by the water-vapor content and
atmospheric conditions
M
Magnetic Annealing
Thermal process involving a ferromagnetic sample in
a magnetic field in which the sample has induced
a direction of easy magnetization (easy axis)
Magnetic Random-Access Memory (MRAM)
Digital memory device composed of ferromagnetic
thin films coupled to current-carrying conductors
used to establish the direction of the magnetization
in the ferromagnetic films. The resistance of the
coupled films is different when the direction of
magnetization in the two ferromagnetic films is
changed
Magnetic Spacing
Spacing between the bottom of the slider and the
center of the ferromagnetic storage layer in
a recording medium characterized by the magnetic
spacing parameter d
Magnetic Transition
In digital magnetic recording, the region between
opposite states of the magnetization in the recording
medium. The length of the transition (l) is l = πa,
where a is the transition parameter
Magnetic Tunneling Junction (MTJ)
MRAM in which the magnetic state of the
ferromagnetic sample is sensed by the change in
resistance of electron current tunneling through a thin
insulating layer when the magnetization in the two
electrodes coupled to the ferromagnetic sample is
changed from parallel to antiparallel orientation
Magnetoresistance
Change in resistance of a ferromagnetic material due
to changes in the orientation of the magnetization with
respect to an induced easy axis. Sometimes referred to
as the anisotropic magnetoresistance (AMR).
Characterized by the change in resistivity with
magnetic field normalized to the nominal resistivity
∆ρ/ρ
Magnetoresistivity (MR)
Change of resistivity ρ in applied magnetic field. For
Si, MR is a diverse tensor reflecting the symmetry of
the CB and VB
Majority Carriers
Electrons in an n-type and holes in a p-type
semiconductor. Majority-carrier mobility is the
mobility of electrons (holes) in n-type (p-type)
material
Media Flux
Product of the remanent magnetization and the
thickness of a magnetic recording film
Media Noise
Noise voltage at the terminals of a read head caused
by fluctuations in the magnetization of the recording
media
Mercury-Sensitized Photo-CVD
Technique for preparing thin films by decomposing
source gas materials by collision with photo-excited
mercury atoms
Mesogen
This is a molecular compound or mixture of
compounds capable of forming a liquid-crystal phase
over a range of temperatures between the crystal and
isotropic liquid phases
Metal Semiconductor Field-Effect Transistor
(MESFET)
Probably the simplest three-terminal device that can
be fabricated on GaAs. The “metal semiconductor”
refers to the gate structure, which is a simple Schottky
barrier. The application of a reverse bias to this gate
produces a depleted region that occludes part of the
cross-sectional area of the channel, and thus modifies
its conductivity
Metallic Nanocomposites
Composite materials made out of metallic quantum
dots embedded in organic or glass hosts
Metastability
A term that refers to the nonequilibrium nature of
glasses or amorphous solids. Amorphous solids have
excess internal energy relative to the corresponding
crystalline state or states of the same material. The
method of manufacture, such as melt quenching,
inhibits a transition to the lowest-energy crystalline
state
Microphotonics
Refers to the chip-scale manufacture of optical and
photonic waveguide circuitry, using processing
techniques borrowed from the microelectronics
industry. Related to this is the need for high-density
integrated optics, as facilitated by high-index-contrast
waveguides and photonic crystals. By usual definition,
microphotonics refers specifically to the monolithic
manufacture of optical and photonic elements on
silicon (CMOS) chips
Glossary of Defining Terms
Miller’s Rule
An empirical rule proposed by Miller in 1964, which
suggests that χ (2) /{χ (1) }3 is nearly constant for all
non-centrosymmetric crystals
Miniband
Interval of allowed energies for carriers in
a superlattice, resulting from the delocalization and
broadening of the quantum-well energy levels
Minority Carriers
Electrons in a p-type and holes in an n-type
semiconductor. Many electron devices work on the
base of minority-carriers transport. Minority-carrier
mobility is the mobility of electrons (holes) in p-type
(n-type) material
MIS
Abbreviation for structure
metal/insulator/semiconductor (see MOS)
Misfit Dislocations
These are dislocations introduced near the boundary
of an epitaxial layer and the substrate, when
a mismatch between the lattice constants exists. The
density of these dislocations is proportional to the
mismatch. Although they run parallel to the boundary,
they can interact and penetrate much of the epitaxial
layer; see threading dislocations
Mixed State
In type II superconductors this state exists between the
lower and upper critical fields. In the mixed state
superconducting and normal regions coexist.
Magnetic flux enters the superconductor in the normal
cores of the flux lines
Mobility Edge
The boundary between localized and delocalized
states in a band
Mobility Gap
Energy separation between two mobility edges of the
conduction and valence bands
Mobility
Parameter defined as the ratio of the carrier velocity
(cm/s) to the electric field through which it is moving
(V/cm). It is expressed in units of cm2 /Vs. At the
microscopic level, it is related to the dominant
scattering time and the effective mass of the carrier.
The notion includes drift mobility µ, which
corresponds to the motion parallel to the field and Hall
mobility µH , which corresponds to motion
perpendicular to the electric field, when a magnetic
field is applied
MOCVD
Technique for depositing thin films of compound
semiconductors from a chemically reactive vapor
phase where at least one of the components is
a metal-organic
Modulation Transfer Function (MTF)
The MTF measures the efficiency of an imaging
system such as a detector to resolve (transfer) different
spatial frequencies of information in an image. In
other words, the MTF is the relative signal response of
the system as a function spatial frequency
Molecular-Beam Epitaxy (MBE)
Low-temperature growth technique for epitaxial films
from atomic or molecular beams from thermal
evaporation sources. It is carried out in ultra-high
vacuum. CBE is a form of molecular-beam epitaxy in
which group III and group V beams are generated
from external gas sources. MOMBE is a form of MBE
where some or all beams are generated from external
gas sources, in III–V MBE only the group III beams,
from metal-organic sources. GSMBE is a form of
MBE where some or all beams are generated from
external gas sources, in III–V MBE only the group V
beams, from hydride sources
Molecular Electronics
Exploitation of organic materials for electronics and
optoelectronics applications. Examples are displays
based on liquid crystals and organic
electroluminescent polymers. In the case of organic
polymers, the area is sometimes referred to as plastic
electronics
Molecular Reorientation
Nonlinear process in which the orientation of
molecules in liquid changes upon illumination with
intense light
Molecularly Doped Polymers (MDP)
Formulations of charge-transport materials dissolved
in a polymer matrix. CTLs of OPCs are typically
MDPs
Monolayer (ML)
A single layer of atoms (in III–V MBE a layer of the
compound or alloy, e.g. a layer of Ga + As)
Moore’s Law
prediction based upon the empirical observation by
G. Moore that the minimum cost of manufacturing
integrated circuits per component actually decreases
with the increase in the number of IC components, and
thus with greater circuit functionality and computing
power. A corollary of this observation is that the
density of integrated circuit transistors will double
roughly every 1.5–2 years (see scaling)
MOS
Abbreviation for a metal/oxide/semiconductor
structure, which is one possible realization of MIS.
The insulator has traditionally been SiO2 (the oxide)
due to superior materials and electrical properties,
resulting in the abbreviation MOS
Moseley’s Law
States that the square root of the frequency of
characteristic X-rays, for certain elements, is linearly
related to the atomic number
MOVPE
Metalorganic vapor-phase epitaxy is
a low-temperature growth technique using metalalkyls
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Glossary of Defining Terms
(and elemental Hg in the case of Hg-based ternary
compounds) as the sources
MPCVD Technique
(Microwave plasma chemical deposition technique)
A technique for film deposition. This is now the most
widely used technique for diamond growth. Energy is
transferred by the microwaves to gas-phase electrons,
which transfer their energy to the gas through
collisions. The gas molecules dissociate and the active
species are formed and the deposition of diamond onto
the substrate immersed in the plasma occurs
Multi-Crystalline Silicon (mc-Si)
Wafers of silicon, cheaper to produce than the
single-crystal silicon wafers but have multiple
single-crystal grains in each wafer
Multiple Quantum Well (MQW)
Structure composed of a stack of QWs separated by
sufficiently thick barriers so that the electron wave
functions and energy levels are localized to each QW
MW
Abbreviation for medium wave, the term for the
transparent atmospheric window between the
wavelengths 3.3 µm and 5 µm. There is a CO2
absorption band around 4.25 µm which divides the
band into two with the better atmospheric
transmission in the 3.3 to 4.2 µm band
N
Narrow Bandgap
Refers to a semiconductor with a forbidden energy
gap of less than about 0.7 eV, making it suitable for
detection in the infrared wavebands
Native Defect
A vacancy, a self-interstitial, an anti-site or any
complex of these
Negative Differential Resistance (NDR)
(see, transferred electron effect). In GaAs, electrons
that undergo the transferred electron effect, are excited
from the primary conduction band minimum where
their effective mass is low to subsidiary minima where
their effective mass is considerably greater. As
a result, although they have greater kinetic energy,
their drift velocity is lower. This, in turn, results in
a reduction of current in the external circuit. The
current–voltage characteristics show a reduction in
current after a critical voltage is applied (although the
ratio of current to voltage will always be positive).
This is NDR. It can be shown that current flow in the
NDR region is unstable and that charge tends to be
transported in groups, resulting in oscillations in the
current flow. This is the Gunn effect and is used in
some microwave sources
Nematic Phase
is the simplest of the liquid-crystal phases; it has
long-range orientational order but is devoid of
long-range translational order
NETD
Noise-equivalent temperature difference is a measure
of sensitivity for a multiplexed infrared detector and is
the change in scene temperature that produces a signal
equivalent to the rms noise level of the detector
Nonlinear Directional Coupler
A device where a part of one of two waveguides is
made out of a nonlinear material. Changing the
intensity of the incident light changes the effective
path length experienced by the waveguided light,
thus controlling coupling between the two
waveguides
Nonlinear Fabry–Perot Interferometer
A device that consists of two mirrors separated by
a nonlinear material. As the refractive index of the
nonlinear material changes with an increased level of
illumination, the effective path length of the resonator
is altered, changing the transmission properties of the
device
Nonlinear Figure Of Merit
A figure of merit that describes the applicability of
a refractive nonlinear optical material in terms of
nonlinear index change and effective absorption
Nonlinear Kramers–Kronig Transformations
A set of two relations that permits calculation of the
real (imaginary) part of nonlinear response at a given
optical frequency given the knowledge of the
imaginary (real) nonlinear response at all other optical
frequencies
Nonlinear Mach–Zehnder Modulator
A Mach–Zehnder modulator in which a part of the
waveguide is made out of a nonlinear material.
Changing the intensity of the incident light changes
the effective path length experienced by the light a the
nonlinear waveguide, controlling transmission
Nonlinear Material Figures Of Merit
A set of metrics that allows us to quantify the
applicability of a nonlinear optical material to optical
switching
Nonlinear Optical Medium
A material whose properties change upon illumination
with intense light
Nonlinear Optical Switching
Switching of optical signals using an
illumination-dependent phase shift of nonlinear
materials
Nonlinear Periodic Structure
A Bragg periodic structure in which at least one set of
layers is nonlinear
Nonlinear Phase Shift
A difference between the phase shift experienced by
intense light and a phase shift experienced by light
which intensity approaches zero
Glossary of Defining Terms
Nonlinear Polarization
Polarization that does not experience purely linear
dependence on the electric field
Non-stoichiometry
Defined as the difference between the total anion and
cation concentrations, hence anion- or cation-rich
n-Type Conductivity
A semiconductor material, with electrons as the
majority charge carriers, that is formed by doping with
donor atoms
Nucleation Temperature
Temperature where stable defect clusters/aggregates
start to form as nuclei
Numerical Aperture
Figure of merit used to described the power of a lens,
depending on the angle of collection of the lens and
the refractive index of the medium in which the lens is
situated
O
Onsager Model
A model that describes the probability of geminate
recombination as a function of applied field with the
efficiency of geminate pair photogeneration and the
initial pair-separation distance as parameters
Optical Absorption Coefficient
4π times extinction index, divided by the radiation
wavelength
Optical Bistability
A phenomenon in which the instantaneous
transmittance of the device depends both on the level
of incident illumination and on the prior transmittance
of the device. Such an element enables all-optical
switches
Optical Constants
The real and imaginary parts of the square root of the
dielectric constant/susceptibility, called the refraction
and extinction index, respectively; they define the
optical properties of bulk material and mesoscale
structures
Optical Emission Spectroscopy (OES)
A technique to determine the plasma parameter and
reactions in the plasma by measuring the emission
intensity of line spectra from the plasma
Optical Gap
(See Bandgap)
Optical Limiter
A device in which the transmittance decreases with
increased level of illumination
Optical Properties of Sample
These include the apparent reflectance, transmittance
and absorbance
Optical Texture
Pattern observed for thin slabs of birefringent material
between crossed polarizers under a microscope. It is
used as a fingerprint to help identify the many
different liquid-crystal phases
Optically Detected Magnetic Resonance
Magnetic resonance observed by optical means,
particularly by detection of electron spin resonance by
monitoring luminescence intensity and polarization,
etc.
Order Parameter
The parameter that measures the extent of long-range
order characteristic of a phase. The orientational order
parameter is the most important for liquid crystals; by
definition it vanishes in the isotropic phase
Organic Photoconductors (OPC)
Single material or a formulated blend of materials that
have photoconductive characteristics
Organic Photoreceptors
Thin-film multilayer devices made from organic
photoconductive materials. These devices are often
called organic photoconductors
Oscillator Strength
Measure of the probability of a transition between
levels; an oscillator strength of 0.01–1 is highly
probable (allowed) and has a short lifetime (ns), one
less than 0.001 is improbable (partially forbidden) and
has a long lifetime (µs–ms)
Oxidation-Induced Stacking Fault
A stacking fault that shows up after wafer oxidation.
During oxidation, Si interstitials are injected from the
wafer surface into the bulk. They aggregate around
oxygen precipitates of a critical size and thereby
squeeze an additional lattice plane (stacking fault)
between two regular lattice planes
Oxygen Precipitates
Aggregates of oxygen atoms that form in
Czochralski-grown crystals due to their relatively
large oxygen content. The silica crucible that holds the
Si melt is slowly dissolved during the growth process
that introduces oxygen into the melt and, hence, into
the growing crystal
P
Paraelectric
Nonpolar phase that transforms into the ferroelectric
phase at the Curie temperature
Partial Response Maximum-Likelihood (PRML)
Recording Channel
Particular form of equalization used in digital
recording channels. The detector is maximum
likelihood
Passivation
Passivation refers to the removal of electrical activity
of a defect, often by trapping a mobile atom of the
opposite electrical type (a donor may trap a mobile
acceptor, for example). The defect now becomes
a complex, consisting of the original defect and the
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Glossary of Defining Terms
new component in close proximity, but without
electrical properties. Unlike compensation, ionized
impurity scattering is reduced by passivation and
carrier mobility is increased
Passive Matrix Addressing
Also known as simple multiplexing, passive matrix
addressing is a technique for writing images onto
liquid-crystal displays. The display elements are
arranged as a matrix of rows and columns, and a series
of voltage pulses are applied to each row in sequence.
Individual pixels are activated by applying a voltage to
the relevant column, such that the sum of the row and
column voltages exceeds the desired switching or
threshold voltage. Each pixel responds to the root
mean square voltage applied during the line-address
time, and unlike the active-matrix addressed displays,
there is no charge-storage facility. Thus, the number of
rows that can be addressed is limited
PECVD Technique
An abbreviation for plasma-enhanced chemical vapor
deposition. Like CVD, this is a technique for thin-film
deposition. In contrast to the CVD technique, in the
PECVD technique the deposition of a film is
a nonequilibrium process. The gas-phase reactions,
which are activated by temperature in the CVD
technique, originate in the PECVD technique from an
interaction of electrons with the gas molecules
injected in the reaction chamber. In the plasma the
dissociation of the gas precursors is obtained by their
collisions with energetic electrons. The products of the
reactions interact with the substrate surface and leads
to the deposition of a thin film. As the dissociation of
the gases is produced by electron impacts, the reactor
and substrate can be kept at room temperature
Penetration Depth (λL )
The characteristic length scale for the penetration of
a magnetic field into the surface layer of
a superconductor
Perfect Diamagnetism (Meissner Effect)
Of the superconducting state is reflected by the fact
that a magnetic field is expelled from the interior of
a field-cooled superconductor as soon as the
superconducting state is reached
Permalloy
Alloy of nickel and iron with approximately 80% Ni
and 20% Fe. Composition of alloy with zero
magnetostriction
Permittivity (ε)
A measure of the polarizability of a dielectric
material, which is frequency dependent. The relative
permittivity of a material is often given by ε or εr ,
such as with the parallel-plate capacitor expression for
capacitance: C = εε0 A/t. (See also dielectric
constant.)
Perpendicular Magnetic Recording
Recording system consisting of write and read head
and a recording media where the magnetization is
perpendicular to the surface of the recording
medium
PES Technique (Photoemission Spectroscopy)
PES is a method to determine the barrier heights of
Schottky contacts and band offsets of semiconductor
heterostructures from energy-distribution curves of
electrons photoemitted from Schottky contacts and
semiconductor heterostructures excited by ultraviolet
light (UPS), soft X-rays (SXPS) and X-rays (XPS)
Phonons
Quantized lattice vibrations in a solid
Phosphorescence
Luminescence with a lifetime 10 ns, typically
involving a metastable state in the pumping cycle
Photo-Thermal Ionization Spectroscopy
A very sensitive technique for the measurement and
identification of shallow impurities in semiconductors.
The measurement is a two-stage process; the
absorption of light excites the electron on un-ionized
donors into a higher level and thermal energy now
ionizes this electron into the conduction band, where it
can be measured as a photo-current. Because the
energy of the optical ionization is dependent on the
donor type, the photocurrent spectrum as a function of
photon energy, displays peaks that are characteristic of
the donors present
Photo-catalysis
An enhancement of the reaction rate on the surface by
shining UV radiation onto the growing film
Photochromic
Temporal coloring induced by (UV) light illumination.
For instance, photo-structural changes of Ag particles,
which are dispersed in oxide glasses
Photoconductivity
The part of the conductivity that is caused by the
absorption of light. Negative values of the
photoconductivity are possible when optical excitation
activates efficient carrier traps. A photoconductive
device uses the change in resistance of a slab of
semiconductor to measure the extra electron–hole
pairs created by the absorption of photons
Photocurrent
The current that is generated as a result of absorption
of light
Photodarkening
Quasi-stable darkening induced by light illumination.
In chalcogenide glasses, it occurs with a red-shift of
optical absorption edge, which is induced through
athermal photo-structural processes. The process,
however, is speculative
Photoinduced Degradation
A deterioration of semiconductor properties by
prolonged light exposure
Photoinduced Discharge Characteristic (PIDC)
Plot of exposed potential versus exposure using either
Glossary of Defining Terms
a continuous exposure or flash exposures of varying
intensity
Photoinduced Effects
Changes in the properties of a glass induced by light,
involving transitions between metastable states of the
glass or changes in defect sites within the glass.
Typically, a laser beam is used to locally modify the
refractive index, density, absorption coefficient, etc. of
the glass (see photodarkening, photo-induced
degradation). These processes are widely used to
pattern photonic structures such as Bragg gratings,
waveguides, and refractive lenses into glasses
Photoisomerization
Light-induced change in the molecular structure of
a molecule
Photoluminescence
Luminescence excited by the external illumination of
the material. It should be distinguished from reflection
and light scattering, which are also caused by external
illumination and are not connected with thermal
radiation of the material too. The criterion to
distinguish these phenomena is the characteristic
decay time after the cessation of the incident light.
While reflection and scattering would decay within
≈ 10−14 s (characteristic time of electromagnetic
oscillations of incident light wave) the
photoluminescence would persist at least more than
≈ 10−12 s (characteristic time of atomic vibrations of
luminescent material)
Photon
A quantum of electromagnetic radiation
Photonic Glass
High-purity glasses in which impurities are controlled
or suppressed at ppm levels. An example is the optical
fiber glass developed at the end of the 20th century,
which is very recent when compared to a long history
of artificial glasses of 5000 years
Photorefractive Beam Fanning
Spreading of an intense light beam due to the
photorefractive properties of a material
Photosensitivity
of an organic photoconductor is a measure of the rate
of photodischarge when exposed to light. Typical
characterizations are the initial slope of the
photodischarge (volts/J) and the energy required for
photodischarge to half the initial surface potential
Photovoltaic Device
Utilizes a p–n junction in a semiconductor to separate
electron–hole pairs (created by the absorption of
photons) to generate a voltage
Photovoltaic Module
A complete encapsulated device suitable for mounting
on a roof or building façade. Modules will often
comprise of a number of cells and typical size is of the
order of 1 m2
Photovoltaic Solar Cell
A semiconductor device for conversion of solar energy
into electricity
Piezoelectric Polarization
Generation of electric polarization in certain dielectric
crystals as a result of the application of mechanical
stress
Piezoelectricity
Property of some crystalline materials, which produce
an electric charge when subjected to an externally
applied force (direct effect). They also deform when
subjected to an external electric field (reverse effect)
Piezoresistivity
Property of certain materials, including thick-film
resistors, whereby an externally applied force gives
rise to a change in resistance
Pinned Film
Coupling of a ferromagnetic to an antiferromagnetic
film resulting in the magnetization of the
ferromagnetic film being constrained to a fixed
direction. The strength of the coupling is characterized
by an exchange field parameter (Hua ) measured in Oe
or A/m
Pixie Dust
Thin layer of Ru as used in synthetic
antiferromagnetic media (SAF)
Planar Lightwave Circuit (PLC)
The industrially established processes for
manufacturing integrated optics devices in
silica-based glasses deposited on silicon wafers.
Typically, the glass layers are deposited by chemical
vapor deposition or flame hydrolysis. These
technologies were developed mainly for applications
in fiber optics, and are widely used to manufacture
wavelength multiplexers
Plasmon
Quantized collective motions of electron gas in
a metal. In a bulk metal, the plasmon propagates as
a longitudinal wave, which may be probed by an
electron beam. In a metal nanoparticle, a transversal
surface plasmon can be excited by light waves
Plastic Deformation
Deformation of a body caused by an applied stress,
which remains after the stress is removed
Plastic Electronics
Use of polymers in electronic and optoelectronic
devices (See also molecular electronics)
Point Defect
Smallest structural element, or imperfection, to cause
departure from a perfect lattice structure, e.g. a dopant
or impurity atom
Poisson’s Equation
A differential equation relating the spatial gradient of
the local electric field to the local space-charge
density
1355
1356
Glossary of Defining Terms
Poisson’s Ratio ν
The ratio of transverse contraction strain to
longitudinal extension strain in the direction of
stretching force. Tensile deformation is considered
positive and compressive deformation is considered
negative. The definition of Poisson’s ratio contains
a minus sign so that normal materials have a positive
ratio
Polarity
Property of a physical system that has two points with
different characteristics, such as one that has opposite
charges or electric potentials
Polarization Ratio
The density of states at the Fermi energy in an energy
band for electrons in a metal with spins parallel
↑
(antiparallel) to the local magnetization is D(E F ) and
↓
D(E F ), respectively. The polarization ratio is
P=
↑
↓
D(E F )−D(E F )
↑
↓
D(E F )+D(E F )
Poles of a Write Head
Structure in a write head that couples the magnetic
fields to the write gap
Polycrystalline Solid
Polycrystalline material is not a single crystal as
a whole, but composed of many small crystals
randomly oriented in different directions. The small
crystals in polycrystalline solids are called grains.
Theses grains have irregular shapes and orientations.
A polycrystalline material has grain boundaries where
differently oriented crystals meet. Polycrystalline
silicon is produced in the form of a ribbon or thin films
Polygonization
The motion of dislocations to form structures that
resemble three-dimensional polygons. In this way,
they minimize their strain energies. Readers are
referred to the many excellent books on materials
science that discuss dislocations and their
interactions
Polymer Thick Films
are those that are cured at much lower temperatures
than their cermet counterparts. The binding matrix is
a polymer material and the resulting films can be used
in flexible circuits
Positron Annihilation
Analytical technique that is sensitive to open defects,
such as vacancies, in a crystal. The lifetime of
positrons is greater when the total number of electrons
is reduced, as happens at vacancies. Measuring
positron lifetime can give semiquantitative estimates
of the concentrations of these defects
Power Stabilizer
Optical device that can provide a fixed output intensity
upon varying input intensity. The principle may be
based on multi-photon absorption, which becomes
efficient when light is more intense
Precursor
Volatile compound containing the element required
for deposition onto the substrate
Process Integration
The carefully engineered combination of materials
and processes to enable the fabrication of an
integrated circuit technology. The careful
consideration of materials properties, device physics
and electrical engineering principles is required for
successful integration of materials into an IC chip
Proper Ferroelectric
Ferroelectric material in which the spontaneous
polarization is the primary order parameter
Pseudo-morphic Layers
True epitaxy only occurs when the lattice constants of
the substrate (material A) and layer (material B) are
equal. If they are different, misfit dislocations or even
gross bending of the structure can occur. In
pseudo-morphic growth, the lattice constants can be
very different. However, before misfit dislocations can
be formed, either the growth of B is stopped or a layer
of the substrate material, A, is grown on top of the
structure. In either case, the structure is stabilized with
material B being severely strained. Manufacturers use
this technique to produce devices with advanced
electrical or optoelectronic properties
p-Type Conductivity
Semiconductor material in which the dopants create
holes as the majority charge carrier. It is formed by
doping with acceptor atoms
Pulse Width
Width of a pulse in a digital magnetic recording read
head when sensing a recorded transition.
Characterized by the 50% width (PW50 )
Pyroelectric Effect
Generation of an electric polarization change or
a charge separation in a material in response to
a change in material temperature
Pyrolytic Boron Nitride (pBN)
This is the favored crucible material for GaAs growth
from the melt and for Knudsen cells for MBE.
Pyrolytic refers to its high-temperature capabilities
Q
Quantum Cascade (QC) Laser
Light amplification by stimulated emission of
radiation (laser) through inter-subband transitions and
unipolar electron transport
Quantum Confined Stark Effect
The change in near-band-edge optical absorption in
quantum wells that takes place when a high electric
field is present
Quantum Dot (QD)
A semiconductor quantum heterostructure that is
quantum confined in all three dimensions, for example
Glossary of Defining Terms
InAs islands embedded in a layer of GaAs and Ge
islands in Si
Quantum Efficiency
Indicates either the probability that the absorption of
a photon will result in the creation of a free electron
and hole or the ratio of the number of luminescence
photons to the number of stimulating photons. When
determined by xerographic discharge of the
photoreceptor QE is a measure of the overall
effectiveness of surface charge neutralization per
absorbed (or incident) photon. It is sometimes called
xerographic gain or supply efficiency. When
determined by spectroscopic methods, such as
fluorescence quenching, it is a measure of charge
generation within the light-absorbing moiety
Quantum Well (QW)
Low-dimensional semiconductor quantum
heterostructure where a thin layer with lower bandgap
is sandwiched between layers (barriers) with higher
bandgap, leading to spatial confinement of carriers
along one dimension for which the energy is quantized
in discrete levels. Carriers have free motion in the
plane perpendicular to the confinement direction. May
be repeated to produce a multiple quantum well
(MQW)
Quantum Well Inter-subband Photodetector (QWIP)
Long-wavelength (IR) detector based on light
absorption through inter-subband electron transitions
in n-doped QWs
Quantum Wire
Semiconductor quantum heterostructure with
two-dimensional confinement of carrier motion.
Carriers have just one direction of free motion
Quantum-Confined Stark Effect (QCSE)
Response of the confined electrons and holes in
a quantum well to a strong DC electric field applied in
the growth direction
Quantum Size Effect
Quantum effect associated with quantization of the
band and level. It is observed in two-, one- and
zero-dimensional systems whose size becomes small
Quasi Particles
Unpaired electrons excited above the energy gap
Quasi-Fermi Levels
Levels that correspond to the energy positions the
equilibrium Fermi level would need to have in the gap
in order to produce equivalent carrier densities to the
ones that are generated by the illumination
R
Radiation Resistance
This is important for solar cells operating in space
where high doses of gamma rays and high energy
particles can significantly degrade the efficiency of the
cells
Radio-Frequency (RF) Circuits
High-speed and microwave analog circuits that
operate in the range 0.1–100 GHz
Reactive Sputtering
Technique for preparing thin films by sputtering with
gas mixture of reactive gas and conventional
sputtering gas such as oxygen and argon
Reactor Cell
Chamber where the precursors react to deposit a film
onto the substrate
Read Head
In magnetic recording the ferromagnetic device used
to generate a voltage proportional to the state of
magnetization in the recording medium
Reciprocal Lattice
Theoretical lattice constructed from a real lattice, such
that any vector from the origin to a diffracted spot is
normal to a particular plane in the real lattice, with
reciprocal length of that plane spacing
Recombination
Process whereby non-equilibrium populations of
electrons and holes return to their equilibrium values.
Depending on whether the recombination rate is
proportional to the excess carrier density or the square
of that quantity, the processes can be referred to as
linear and quadratic, or alternatively as
monomolecular and bimolecular recombination.
Radiative recombination refers to the transfer of at
least some of the energy of the excess carriers into
photons. Non-radiative recombination involves only
the production by lattice phonons (heat)
Reflectometer
Instrument used for reflecting light off the substrate to
monitor the growth process. This is normally achieved
through detecting the interference modulation of the
light intensity from a growing film
Reflow
Process of heating a glass above its glass-transition
temperature, to the point that its viscosity is
sufficiently reduced to enable the material to flow. In
combination with surface tension effects or other
external forces, reflow is often exploited in the
reshaping of optical devices
Remanent Magnetization
is magnetization that remains in a sample after the
magnetic fields are removed
Remanent Polarization
Dielectric polarization that remains in a ferroelectric
material after an electric field has been applied
Resistivity
Parameter of a semiconductor that depends on the
free electron and hole densities (cm−3 ) and their
respective mobilities (cm2 /Vs) and is expressed in
units of Ω cm. It is the reciprocal of conductivity
and it depends strongly on temperature in
a semiconductor
1357
1358
Glossary of Defining Terms
Resolution
The smallest separation of two points in an object that
can be distinctly reproduced within an image
Resonant Nonlinear Response
The nonlinear response taking place in the absorbing
spectral region
Responsivity
Signal term often measured using a two-temperature
black body. Units can be V/W (used for
photoconductors) or V/photon (often used for
multiplexed photodiodes)
Retrograde Solidus
Describes the shape of the solidus when it shrinks as
the temperature is reduced. In GaAs, the increased
width of the solidus at high temperatures indicates that
concentrations of Ga or As, in excess of stoichiometry,
can exist in the solid crystal. These concentrations
must reduce as the crystal cools because of the
retrograde solidus
RHEED
Glancing-angle electron diffraction technique,
sensitive to surface reconstruction and morphology.
Key in situ analytical technique in MBE
ROIC
Abbreviation for readout integrated circuit, commonly
used to describe the silicon chip on which the detector
material is mounted. The role of the ROIC is to
integrate the signal, perform some signal processing
and readout the array. Other terms are: multiplexer or
mux
R–T Method
Defining the optical constants, based on two equations
connecting the formers to the reflectance and
transmittance of the slab sample of material under
measurement
Rutherford Scattering
Elastic scattering of electrons due to an electrostatic
interaction with the nucleus and surrounding electrons
of an atom
S
Saturated Vapor Pressure (SVP)
Partial pressure of a substance in equilibrium with its
liquid, so the partial pressure is determined solely by
the temperature of the liquid and vapor
Saturation Intensity
Intensity at which the effective absorption decreases to
a half of its initial value
Saturation Magnetization
Maximum magnetization that a ferromagnetic sample
can attain in magnetic fields larger than the coercive
field
Saturation of Absorption
Resonant nonlinear process in which absorption
decreases with increased level of illumination
Scaling
Calculated reduction of integrated circuit element
dimensions according to physical and engineering
principles and constraints, as well as economic
considerations (See Moore’s Law)
Scanning Probe Microscopy
Generic term given to microscopy techniques that use
a scanned micro- or nanoscale tip in immediate
proximity to a surface to image topography or other
physical features with almost atomic resolution. The
main types are atomic force microscopy (AFM) and
scanning tunneling microscopy (STM)
SCH Laser
Separate confinement heterojunction laser. In the SCH
laser the optical and electrical confinements are
achieved separately by altering the thickness and the
alloy composition of the cladding layers
Schottky Contacts
Metal–semiconductor contacts are also named
Schottky contacts
Schottky–Mott Rule
Schottky–Mott rule equates the barrier heights of
n-type (p-type) Schottky contacts with the difference
of the metal work function and the electron affinity
(ionization energy) of the semiconductor. The rule is
incorrect since it does not consider the intrinsic
interface-induced gap states
Screen
Mask used to define the desired thick-film pattern. It is
usually made of stainless steel, polyester or nylon
Screen Printing
Method by which thick films are deposited onto
substrates. See also antiferromagnetically coupled
media (AFM)
Secondary Electrons
Low-energy (< 50 eV) electrons that escape from the
near sample surface, used to form topographic images
Secondary-Ion Mass Spectrometry (SIMS) and Glow
Discharge Mass Spectrometry (GDMS)
Mass-spectrometric techniques that are well suited
for the chemical analysis of semiconductors. In
addition to being extremely sensitive to most
impurities, they are quantitative and can give valuable
information regarding the distributions of
concentrations with depth. In SIMS, high-energy
primary ions are focused on the sample surface. These
sputter atoms from the material under investigation.
Those that are charged are passed into a mass
spectrometer for analysis. In GDMS, the sputtering is
accomplished by a glow discharge. SIMS is, by
convention, generally classified as dynamic, in that the
material surface layers are continually removed as
they are being measured, and static, in which the ion
dose during measurement is restricted to less than
1016 ions/m2 in order to retain the surface in an
essentially undamaged state
Glossary of Defining Terms
Segregation Coefficient, k
In growth from the melt the incorporation of an
impurity into the crystal depends on the equilibrium
ratio of the solubilities in the melt and the solid. For
a dilute solution, this ratio is given by the ratio of the
equilibrium value of impurity concentration at the
solidus and the liquidus at the growth temperature.
This ratio is the segregation coefficient, k. For most
impurities, k is less than unity and the growing crystal
contains a lower impurity concentration than in the
source melt. The exploitation of this fact has resulted
in the purification technique of zone refining
Selection Rule
Quantum-mechanical rule based on wave-function and
operator symmetry that determines oscillator strength;
typically set by parity or angular-momentum
considerations
Selective Epitaxy
Growth of a single-crystal layer in a window without
any deposition on the surrounding mask layer
Selenization
Process of forming the CIGS or CIS layer by exposing
a copper, indium and gallium precursor layer to Se to
form the alloy
Self-Assembly
Spontaneous formation of a layer of organic material
on a solid substrate surface. The process usually takes
place by immersing the substrate into a solution of the
organic compound. The driving force for the
self-assembly can be chemical and/or electrostatic
attraction
Self-Defocusing
A nonlinear process associated with negative
refractive nonlinearity that results in spatial spreading
of intense light
Self-Focusing
A nonlinear process associated with positive refractive
nonlinearity that results in focusing of intense light
Semi-Insulating
This is a term given to semiconductors whose
resistivity lies above about 106 Ω cm. In GaAs,
semi-insulating properties normally lie in the range
of 107 –108 Ω cm
Semiconductor Detector
Device that converts the incident photons directly into
electrical pulse
Semiconductor Nanocrystals
Composite materials made out of semiconductor
quantum dots embedded in organic or glass hosts
Shallow-Energy-Level Dopant
Doping impurities whose energy level lies very close
to the conduction or valence band for donors or
acceptors
Shear Modulus
Sometimes also called the rigidity, relates stress and
strain according to Hooke’s law and is a measure of
a material’s resistance to shearing stress. The shear
modulus therefore has units of pressure
Sheet Resistance
Resistivity of a semiconductor sample divided by
its thickness, measured in Ω /square. It is commonly
used by integrated circuit designers when designing
resistances by specifying the number of required
squares required to give a certain value of
resistance
Shields
Soft ferromagnetic films used to direct the flux from
a recording layer away from sensor films in a read
head
Short-Range Atomic Structure
Atomic bonding structures within a scale of ≈ 0.5 nm,
which are characterized by coordination number (the
number of nearest-neighbor atoms), bond length, and
bond angle. It is demonstrated for such simple glasses
as SiO2 that the short-range structure is nearly the
same with that in a corresponding crystal
Signal Decay Rate
Rate (R) at which the amplitude of a signal read back
from a recording system decays with time
A(t)
A(t ) −1
0
R = 100 log(t/t
0)
Single-Layer Organic Photoconductor
A photoconductor with an architecture where the
charge-generation and charge-transport functions are
combined into a single layer
Slider
In a disk drive, the structure used to support on an air
bearing the write and read heads over the recording
medium
Sliding Boat
Liquid-phase epitaxy technique in which the substrate
is slid under the melt in a horizontal orientation
Slope Parameter
(In perpendicular magnetic recording) The slope of
the magnetization curve at the coercive field times
dM
4πα = 4π dH(H=−H
c)
Slush
Homogeneous charge of a ternary is held across the
liquidus–solidus gap with the lower end solid, the
upper end liquid and the central section in a slushy
state, during recrystallization
Smectic Phase
Liquid-crystal phase with some long-range
translational order in addition to the long-range
orientational order of a nematic. The constituent
rod-like molecules are arranged in layers giving
translational order in one dimension
Soft Underlayer (SUL)
Magnetically soft (low-coercivity) film underneath the
recording layer in a perpendicular magnetic recording
system. Used as a low-reluctance path for the flux
from the write head
1359
1360
Glossary of Defining Terms
Solar Cell
Semiconductor device that converts the energy of
sunlight into electric energy. Also called photovoltaic
cell
Solid/Liquid/Gaseous Phase Equilibria
These phase equilibria are essential for understanding
both the various growth techniques used and in
understanding post-growth heat treatments, i. e.
cool-down after growth and subsequent annealing
stages
Solidus
In an equilibrium phase diagram, the solidus is the line
below which all the components are solid
Solitonic Propagation Of Pulses
Propagation of pulses characterized by a lack of
temporal pulse spreading
Spatial Frequency
Spatial frequency is the reciprocal of a spatial
dimension (e.g., height x or width y in
two-dimensional image) similar to the temporal
frequency, which is the reciprocal of time. However,
the unit of spatial frequency is preferably expressed as
line pairs/mm (lp/mm), instead of cycles/mm
Specific Heat
(also called the specific heat capacity). Amount of heat
required to change a unit mass (or unit quantity, such
as mole) of a substance by one degree in temperature
Spherical Aberration
A blurring of resolution due to the spread of path
lengths of rays traveling from an object to the image
plane, arising from a variation of the focal length of
a lens as a function of distance from the center of the
lens
Spin Valve
Read head that uses the giant-magnetoresistive effect
in three metallic films: the ferromagnetic free film,
a non-magnetic spacer film and a ferromagnetic
pinned film
Spontaneous Polarization
The electric polarization that a substance possesses in
the absence of an external electric field
SPRITE
Abbreviation for signal processing in the element:
a device used in the UK common module camera. It
relies on a strip of CMT with a high voltage bias to
drift photon generated holes at the same speed as the
image is scanned, so resulting in an amplified signal at
the end of the strip
Sputter Depth Profile
Compositional depth profile obtained when the
surface composition is measured as material is
removed by sputtering. Note: in some analytical
methods such as SIMS, the sputtering is often
accomplished by the ion beam used for analysis, but in
other methods an ion beam may need to be added
Sputtering
Process in which atoms and ions are ejected from the
sample as a result of particle bombardment
Squeegee
Device used to transfer the thick-film paste through
a screen and onto the substrate
SRAM
Static random-access memory
SSR
Solid-state recrystallization is a growth technique that
produces a homogeneous but polycrystalline charge
that is subsequently recrystallized in the solid state to
produce multi-grained material
Stepanov Technique
Crystals are pulled from a crucible containing
a crystal-shaped aperture
Stoichiometry
State of a perfect compound where the ratio of the
numbers of atoms of the elements is a simple fraction.
In GaAs, for example, stoichiometry exists when the
number of As and Ga atoms are equal
Stokes Shift
Difference in energy between the maximum of the
emission spectrum and the maximum of the excitation
spectrum
Strain (ε)
Defined in elementary form as the change in length
divided by the original length., it can be thought of as
the movement of one corner of a cubic box from its
initial position under stress
Strained Quantum Well
QW layer grown on a substrate with a different lattice
constant, resulting in a significant strain of the QW
layer lattice
Stress
Force per unit area provided either by gravity or by the
flow of viscous fluid
Strong Anchoring
Strong anchoring of the director at a surface parallel to
the easy axis is said to occur when an applied field is
unable to alter the orientation of the director at the
surface but can in the bulk
Structural Relaxation
Essentially an aging effect associated with glasses.
Because glasses are metastable materials with random
network structures, they are inherently subject to
short- or long-term changes in material properties.
Often, structural relaxation is manifested by a change
in specific volume (densification) at fixed temperature
versus time. The rate of such changes is extremely
sensitive to the difference between the glass transition
temperature and the observation temperature.
Structural relaxation can be induced rapidly by an
annealing step, in which the glass is heated near its
glass-transition temperature for some period of time
Glossary of Defining Terms
Substitutional Impurities
Impurities that replace the crystal’s base atom at that
base atom’s lattice position
Substrate
Base material onto which a film is deposited.
Examples of typical substrates include materials such
as alumina, beryllia, aluminum nitride, silicon,
insulated steels and various plastics. In epitaxial
processes, substrates are normally near
lattice-matched pieces of material of a sufficiently
large area for use in the various epitaxial growth
processes, normally from similar, i. e. common-cation,
ternary systems, e.g. CdZnTe for CMT
Superconductors of Type I
Characterized by the fact that normal and
superconducting regions cannot coexist in these √
materials. The value of κ = λL /ξ is smaller than 1/ 2
Superconductors of Type II
√
Type II superconductors, for which κ = λL /ξ > 1/ 2,
show perfect diamagnetism only below the lower
critical field Bc1 . Between the lower and the upper
critical fields type II superconductors are in the mixed
state. Magnetic flux enters the superconductor via the
normal conducting cores of the flux lines
Supercooling Temperature
Difference between the glass-transition temperature
and the in-use temperature for a glass-based device.
For a large (small) supercooling temperature, the
structural relaxation rate is low (high)
Superlattice (SL)
Structure of repeated QWs with thin barriers allowing
the coupling of wave-functions from adjacent QWs
and the subsequent delocalization of the energy levels
Superlattice Avalanche Photodiode (SL-APD)
Avalanche photodiode architecture where an SL is
incorporated in the carrier multiplication region for
the purpose of reducing the dark current as well as the
excess noise factor
Superparamagnetism
In small ferromagnetic particles the magnetization can
flip from one state to the opposite state under thermal
excitation. This behavior is similar to a paramagnet.
The resistance of the particle to switching is
characterized by a thermal stability factor = Kk uTV ,
B
where K u is the uniaxial anisotropy factor for the
particle, V is the particle volume, kB is the Boltzmann
constant, and T is the absolute temperature
Supersaturation
Ratio between the species concentration and its
solubility limit/equilibrium concentration at a given
temperature when this ratio is larger than 1
Superstrate
Describes the thin-film configuration where the glass
substrate acts as the window for solar radiation and
therefore needs a TCO layer before the photovoltaic
structure can be deposited
Surface-Mount Devices (SMDs)
Electronic components that are attached to the surface
of a circuit board as opposed to having through-hole
connections. They are a characteristic feature of
a hybrid circuit
Surface Passivation
Semiconductor surfaces are often electrically active
and appear to be covered with a high density of
deep-level states. These can greatly affect the
properties of a device. Fortunately, it is often possible
to treat the surface to substantially reduce this density
to values that do not affect device operation. This is
surface passivation. In GaAs, passivation is often
accomplished by covering the surface with a layer of
GaAlAs. Also, see passivation
Susceptor
This is normally made of high-density graphite and is
used to transfer the heat from the heater (possibly RF
coupling straight into the susceptor) to the substrate
SW
Abbreviation for short wave, often used for
wavelengths between 1.0 µm and 3 µm. The
atmosphere is transparent in relatively narrow bands
within the SW region, the most common one is
between 2.0 and 2.25 µm, although 1.5 µm is also
important as this is the wavelength for eye-safe lasers
Synthetic Antiferromagnet
Sequence of films:
antiferromagnet/ferromagnet/ruthenium/ferromagnet.
An example is: MnFe/Co/Ru/Co. With a thin Ru film,
the final ferromagnetic film is antiferromagnetically
coupled to the first ferromagnetic film. The coupling
between the two ferromagnetic films is characterized
by the exchange coupling parameter J12 (erg/cm3 or
J/m3 )
Synthetic Ferrimagnetic Media (SFM)
Magnetic recording media in which there are two
ferromagnetic layers of unequal thickness coupled by
a thin layer of ruthenium (Ru), sometimes referred to
as “Pixie Dust”. The two layers are antiferromagnetically coupled. The coupling between the
ferromagnetic films is characterized in terms of the
antiferromagnetic coupling between the thinner layer
(layer 2) and Ru and the media flux from that layer by
an exchange magnetic field Hex = Jex,2 /M2 t2
T
T Nonlinear Figure of Merit
Figure of merit that describes the applicability of
a refractive nonlinear optical material in terms of the
Kerr coefficient and two-photon absorption
Tail States
Localized states in the tail of band, i. e. conduction
band and valence band, which generally have an
exponential density-of-states function
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Glossary of Defining Terms
Tauc Gap
Tauc discovered that, in many chalcogenide glasses
such as As2 S3 , optical absorption spectra α around the
fundamental edge can be fitted as α~ω ∝ (~ω − E g )2 ,
where E g is called the Tauc gap. The energy is often
used as a measure of optical bandgap, while its
theoretical interpretation is not conclusive
Technology Node
Minimum half-pitch of metal interconnect is most
representative of the process capability enabling
high-density (low cost/function) integrated circuits
and is selected to define an ITRS technology node. For
each node, this defining metal half-pitch is taken from
whatever product has the minimum value. Historically,
DRAMs have had leadership on metal pitch, but this
could potentially shift to another product in the future.
Other parameters are also important for characterizing
IC technology. For example, in the case of
microprocessors (MPUs), physical bottom gate length
is most representative of the leading-edge technology
level required for maximum performance. Each
technology node step represents the creation of
significant technology progress in metal half-pitch –
approximately 70% of the preceding node, 50% of
two preceding nodes. (From [IRTS 2003])
Temperature Coefficient of Resistance (TCR)
Denotes the sensitivity of a resistor material to
changes in temperature. It is usual to quote TCR in
terms of parts per million (ppm) per ◦ C
Tensile Strain
Type of strain obtained when a strained Si layer is
grown on a relaxed Si1−x Gex layer
Ternary and Quaternary Alloys
These are alloys containing three or four components,
respectively. GaAlAs and GaAlAsP are examples
Thermal Budget
Term describing the temperature–time product
associated with an IC annealing process step. Material
stability and morphology is typically very sensitive to
annealing temperature for a period of time
Thermal Conductivity
(heat conductivity) Heat flow across a surface per unit
area per unit time, divided by the negative of the rate
of change of temperature with distance in a direction
perpendicular to the surface
Thermal Expansion Coefficient
Fractional change in length or volume of a material for
a unit change in temperature
Thermal Nonlinearities
Nonlinear effect associated with heating of the
materials by intense light
Thermally Stimulated Current (TSC) spectroscopy
TSC is a useful technique for assessing concentrations
of deep levels in high-resistivity semiconductors.
These levels are filled optically with light above the
bandgap energy. They are emptied sequentially, with
the sample under bias, as the sample temperature is
raised. Defects of different ionization energies
produce separate peaks in the graph of current as
a function of temperature
Thermistors
Thermally sensitive resistors that exhibit a change in
resistance when the temperature is altered. The most
common forms have a negative TCR, meaning that the
resistance decreases as the temperature increases
Thermomechanical Fatigue
Occurs when materials with different CTE are joined
and used in an environment that experiences cyclic
temperature fluctuations resulting in imposed cyclic
strain that results in damage to the joined materials
Thermophotovoltaic (TPV)
Absorption of solar radiation and re-emission of
infrared radiation that is then converted into electricity
by absorption in a narrow-bandgap cell
Thermotropic
Liquid crystals are those where the transition from one
phase to another occurs on changing the temperature
Thick Film
Layer deposited onto a substrate by the process of
screen printing
Threading Dislocations
This term is applied to dislocations that are formed at
an interface and that thread their way into the epitaxial
layer
Threshold Voltage (V th )
Voltage at which an inversion layer forms in the
semiconductor substrate of an MIS structure. For
applied voltages beyond this threshold, the transistor
turns on, i. e. a conducting channel is established
between the transistor source and drain, as observed
by the increase in drive current
Time Division Multiplexing
Multiplexing technique used in modern optical
networks that allows close spacing in time of bits in
a single channel
Time-Domain Charge Measurement (TDCM)
TDCM is a rapid technique for the non-contacting
measurement of electrical resistivity in SI materials.
Its speed and high spatial resolution allows TDCM to
be used in a mapping system
Tipping
Liquid-phase epitaxy technique in which the melt is
moved over the substrate in a tipping furnace
Transferred Electron Effect
This is a somewhat unusual effect where
conduction-band electrons can exist in alternative
conduction-band states. In GaAs, the lowest
conduction-band minimum corresponds to zero
electron momentum. The application of an electric
field can excite electrons into subsidiary minima of
somewhat greater energy from where they will relax
back to their original states. If the effective mass of the
Glossary of Defining Terms
electrons in the subsidiary minima is greater than that
in the primary minimum, negative differential
resistance can be realized. This effect can be found in
GaAs, InP and certain alloys
Transistor
A three-terminal device in which the current flow
between two terminals (called the source and drain
regions) is controlled by the voltage applied between
a third terminal (the gate electrode) and one of the two
terminals
Transit Time
Refers to the difference in time between the moment
a charge carrier is generated at one end of the sample
and its arrival at the other end. It is the primary result
in time-of-flight experiments. In xerography, transit
time is the time for a photoinjected carrier to traverse
the charge-transfer layer
Transparent Conducting Oxide (TCO)
Thin layer of highly conducting material that is used
as the front contact in thin-film solar cells. The
requirement of high optical transmission over a wide
spectral range is important to allow as much of the
sunlight through to the absorber layer
Transverse Magnetic Bias Film
In a magnetoresistive head, an antiferromagnetic film
coupled to the pinned film to maintain the
magnetization of the pinned film in a direction
transverse to the magnetization of the recording film
Trapping Centers
Irregular sites in the photoconductor with localized
electronic energy levels inside the bandgap. Such sites
will trap charge carriers and thus inhibit electrical
conduction
Traveling Heater Method
A molten zone is made to migrate through
a homogeneous solid source material
Trimming
Process by which the value of thick-film elements can
be adjusted. Usually achieved by using a laser or air
abrasive jet
Tunneling Magnetoresistance (TMR)
With two ferromagnetic films coupled by a thin
insulating layer, electrons can tunnel through the
insulating layer and the magnetoresistance coefficient
is given in terms of the polarization ratio for the two
2P1 P2
contacts as ∆R
R = 1−P1 P2 .
Tunneling Conduction
Process for charge conduction where the charge
carriers pass through an energy barrier by
quantum-mechanical tunneling
Twin Crystal
Crystal having two or more crystals or crystal sections
that, when regularly positioned, are in reverse position
relative to the other sections
Two-Photon Absorption
Nonlinear process in which a simultaneous absorption
of two photons results in an electronic transition
U
UHV
Ultra-high vacuum is a vacuum better than 10−9 Torr
Ultrafast Nonlinear Response
Nonlinear response taking place in the non-absorbing
spectral region
Underfill
Dielectric composite organic material that is bonded
between the chip and substrate of a flip-chip device to
help mechanically interlock the chip to the substrate.
The underfill material is typically a silica-filled
anhydride resin polymer
Uniaxial Anisotropy
Magnetic anisotropy along one direction in
a ferromagnetic material and characterized by
a uniaxial anisotropy parameter K u (erg/cm3 or J/m3 )
Uniform Planar Alignment
of the director is when the director is parallel to the
surface and to a particular direction in the surface. This
has also been referred to as homogeneous alignment
Unipolar Avalanche Photodiode (UAPD)
QWIP detector employing avalanche multiplication of
only one type of carrier via intra-QW impact
ionization by carrier–carrier scattering
Upper Critical Field (Bc2 )
The highest magnetic field allowing the existence of
the superconducting mixed state in the type II
superconductor considered
V
V/I boundary
Denotes the spatial location of the transition from the
vacancy-dominated region to the Si interstitial
dominated region and vice versa
Vacancy
Regular lattice site from which the host atom is
missing. Anion (cation) vacancies are generally
donors (acceptors)
Valence Band
Highest range or band of energies in a semiconductor
where electrons are normally present at zero
temperature. When electrons are promoted from this
band, holes are left behind that contribute to the
electrical conductivity
Vapor Growth Techniques
Growth takes place via a vapor phase: particularly
useful for high-melting-point materials, or those with
high partial pressures of one constituent, e.g. ZnS
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Glossary of Defining Terms
Vapor-Phase Epitaxy (VPE)
This is a form of epitaxy where the components of the
layer to be grown are transported to the substrate as
a vapor. Decomposition of these components to
produce the layer occurs because the substrate is
heated, often on a support called a susceptor. The
different types of VPE are discussed in the text
(VCSEL)
Vertical-cavity surface-emitting laser. One of the more
modern forms of semiconductor laser, employing the
high gain of quantum wells in a low-loss optical cavity
Vegard’s Law
States that the lattice parameter of an alloy material is
given by the concentration weighted average of the
constituents
Vehicle
Liquid component of the thick-film paste. Typically
contains a resin dissolved in a solvent. It is removed
during the drying and firing processes
Verneuil Technique
Rapid growth method used for many
high-melting-point materials, mainly oxides
Vertical-Gradient Freeze Technique
Similar to Bridgman but freezing is controlled by
moving a temperature gradient along a stationary
crucible
Vertical Transport
Mechanisms of carrier transport parallel to the growth
direction in a semiconductor quantum-confined
structure
Vertical-Cavity Surface-Emitting Laser (VCSEL)
QW diode laser emitting through its top
semiconductor surface
VI Recombination
Mutual annihilation between vacancies and Si
interstitials
Virtual Gap States
The virtual gap states are the solutions of
Schrödinger’s equation for complex wave vectors in
the energy gap. The continuum of these virtual states
is the source of real impurity states in the bulk as well
as of surface states and the interface-induced gap states
at real surfaces and interfaces, respectively, provided
the corresponding boundary conditions are considered
Void
see COP
VPE
A general term used to describe the deposition of an
epitaxial thin film from the vapor phase
W
W Nonlinear Figure of Merit
Figure of merit that describes the applicability of
a refractive nonlinear optical material in terms of
nonlinear index change and linear absorption
Wavelength Division Multiplexing
Multiplexing technique used in modern optical
networks that involves sending many signals in
parallel at closely spaced wavelengths along the same
fiber
Weak Links
Large-angle grain boundaries in cuprate
superconductors, which act as barriers for the
supercurrents
Web Photoreceptors
Devices where the layers are coated on an insulating
polymeric support and subsequently fashioned into
a loop
Wire Bonding
Process where a thin wire (can be less than 25 µm)
made of Au or Al is bonded to the surface of an
integrated circuit and then to a pad or a leadframe in
the package
Work Function
The energy (usually measured in electron volts)
needed to remove an electron from the Fermi level in
a solid to outside the surface
Write Efficiency
Ratio of the magnetic field times write gap to the
magnetomotive force (turns times current) in the write
coil
Write Gap
Region in a write head that generates the magnetic
fields that couple to the recording medium.
Characterized by the gap length g
Write Head
In magnetic recording the ferromagnetic device used
to generate magnetic fields from current that can
switch the state of the magnetization in the recording
medium. In disk drives the ferromagnetic device is
made using thin films
Wrong Bond
Homo-polar bonds in stoichiometric glasses, such as
As–As in As2 S3 . The defective bond nominally does
not exist in the corresponding crystal. However,
specifically in covalent glasses such as As2 S3 , the
bond exists with a concentration of ≈ 1%, which
depends upon preparation methods and so forth
Würtzite Structure
Comprises two interpenetrating close-packed
hexagonal lattices, one for cations and the other for
anions. Each anion (cation) has four cation (anion)
nearest neighbors. In principle diffusion should be
anisotropic but meagre available evidence indicates
only slight effects
X
Xerographic Discharge
Time-dependent decrease in surface potential with
exposure of a charged OPC
Glossary of Defining Terms
Xerographic Gain
or quantum efficiency of supply is the fractional
number of surface charges neutralized per absorbed
photon
Xerography
Name coined by Chester Carlson for
electrophotography using dry powder marking
particles
X-Ray
Form of energetic electromagnetic radiation of
wavelength ≈ 0.1 nm
X-Ray Diffraction
A highly sensitive technique for measuring the lattice
constant of crystalline solids, see B K Tanner and
D. K Bowen, 1980
X-Ray Photoelectron Spectroscopy (XPS)
Method in which an electron spectrometer is used to
measure the energy distribution of photoelectrons and
Auger electrons emitted from a surface irradiated by
X-ray photons
X-Ray Sensitivity
The X-ray sensitivity of a photoconductive detector is
the collected charge per unit area per unit exposure of
radiation
X-Ray Topography
This is a method for sampling the diffraction condition
of X-rays from a surface in order to observe changes
in lattice constant. The X-rays are scanned over the
surface and an image is built up from changes in the
fraction diffracted at a particular angle. Changes in
lattice constant resulting from strain or changes in
composition can be imaged in this way
Y
Yield Strength
Applied stress (in pounds per square inch or psi in the
English system, megapascals or MPa in the metric
system) under which an object experiences plastic
deformation
Young’s Modulus
Ratio of a simple tension stress applied to a material to
the resulting strain parallel to the tension. Therefore
Young’s modulus has units of pressure
Z
Zinc-Blende Structure
A crystal structure that has two interpenetrating
face-centered cubic lattices, one for the cations and
the other for anions. Each anion (cation) has four
anion (cation) nearest neighbors. Diffusion is isotropic
Zone Refining
Technique used to repeatedly pass zones of molten
material through a solid bar in order to purify it, either
for use directly in applications or to produce pure
starting materials, e.g. elements for compound
semiconductors
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