FUNDAMENTALS OF ELECTRONICS DEVICES
NEC 302
ASSIGNMENT 1
Q1 : Describe briefly the lattice structure of Si.
Q2: Derive an expression for the thermal equilibrium concentration of holes in the
valence band of a semiconductor.
Q3: What do you understand by space lattice? Describe briefly the seven systems of
crystals.
Q4: Compare and explain electrical conductivity of metals, semiconductors and
insulators using energy band diagram.
Q5: Briefly discuss the technology for device fabrication.
Q6: Discuss in brief about planer technology of device fabrication.
Q7: Define Fermi level for metal. Show that for intrinsic semi conductor Fermi level is
midway between conduction and valence band. Show the location of Fermi level for an
N-type semiconductor .
Q8: Discuss the effect of temperature on semiconductors.
Q9: Describe the Hall effect. What properties of a semiconductor are determined from
the Hall effect experiment.
Q10: The energy distribution function ℓE is given by the product of two factors [ ℓE =
N(E).f(E)]. What is the interpretation to the given to each of these factors.
Q11: Prove that the concentration of free electrons and holes in an intrinsic
semiconductors is –
n= Nc.exp-(Ec-EF)/kT and p=Nv.exp-(EF-EV)/kT
Q12: Prove that Fermi level in N-type semiconductor given byEF=EC -- KT.log(Nc/ND) and in p-type
FUNDAMENTALS OF ELECTRONICS DEVICES
NEC 302
EF=EV + KT.log(NV/NA)
Q13: Define atomic radius. Calculate the atomic radius in case of simple cubic, FCC
and BCC lattices.
Q14: What are miller indices? How are they calculated that describes a plane in a
crystal? What is the importance of Miller indices?
Q15: What do you mean by packing density or packing factor? Obtain an expression
for it.
Q16: What is co-ordination number? Calculate co-ordination number for simple cubic
lattice.
Q17: Determine the Miller Indices of a set of parallel plane which make –
(i)
(ii)
Equal intercept along the three axes
Intercept of 2a, 3b and 6c.
Q18: The lattice constant for a cubic lattice is a. deduce the spacing between (011),
(101) and (112) planes.
Q19: Determine the interplaner spacing between (200), (220) and (111) planes in FCC
structure. The atomic radius is 1.246 Ǻ.
Q20: Find the dispersion relation for a free electron, and, thus, observe the relation between its rest mass
and effective mass
Numerical
FUNDAMENTALS OF ELECTRONICS DEVICES
NEC 302
FUNDAMENTALS OF ELECTRONICS DEVICES
NEC 302
ASSIGNMENT 2
1. What do you mean by optical absorption? Define absorption coefficient.
2.
3.
4.
5.
What is steady state carrier generation? Prove that
What is continuity equation? Derive the equation
Explain diffusion length. Discuss its physical significance.
What is Einstein relation? Develop expression to establish relation between
diffusion coefficient and mobility of carrier or
Obtain the relation
6. What type of semiconductor material is suitable for luminescence effect?
Explain excitation and recombination of photoluminescence with trap level for
electrons.
7. What is meant by carrier life time? How does direct recombination lifetime
differ from indirect recombination life time?
8. What do you mean by diffusion of carriers? Discuss the diffusion process.
9. Define the following terms –
a. Photoluminescence
b. Photoconductivity
c. Cathodoluminescence
d. Phosphorescence
e. Electroluminescence
f. Fluorescence
10. A 0.46 micrometer thick sample of GaAs is illuminated with monochromatic
light of 2 eV. The absorption coefficient α is 5X104 /cm. The power incident on
the sample is 10 mW.
a. Find the total energy absorbed by the sample per second.
b. Find the ratio of excess thermal energy given by the electrons to the lattice
before recombination.
FUNDAMENTALS OF ELECTRONICS DEVICES
NEC 302
11.A section of silicon device is kept at room temperature. This section is doped
with 1015 /cm3 of acceptor atoms. A stream of minority carriers is injected at x=0
and their distribution in the sample is assumed to the linear; decreasing from a
value of 1011 /cm3 at x=0 to the equilibrium value at x=10 µm. Determine the
diffusion current density of electrons. Given the electron mobility in the Pregion as µe =1331 cm2/V-s and KT/q=0.0259 V.
12.Find the diffusion coefficient of electrons and holes of a silicon single crystal at
27oC. If the
mobility of electron and holes are 0.17 and 0.025 m2/V-s,
respectively at 270C.
13.In an N-Type GaAs crystal at 300 K the electron concentration varies along the
x axis as –
N(x) =1016 e-x/L /cm3 ;
x>0
Where L=1 µm,
Calculate the diffusion current density at x=0, if the electron diffusion
coefficient is 220 cm2/s.
14. Calculate the approximate donor binding energy for Si ( r = 11.7, = 1.18).
FUNDAMENTALS OF ELECTRONICS DEVICES
NEC 302
ASSIGNMENT 3
1. In a p+-n junction, the n-doping Nd is doubled. How do the following change if
everything else remains unchanged?
a. Junction capacitance
b. Built in potential
c. Breakdown voltage
d. Ohmic losses
2. Derive an expression for the contact potential in case of p-n junction.
3. Derive an expression for the total width of transition region.
4. What do you mean by forward and reverse biased junctions? Give a qualitative
description of current flow at a junction.
5. What is zener effect? Explain the function of a zener diode and draw its
characteristics.
6. Find an expression for the electron current in the n-type material of a forward
biased p-n junction.
7. Distinguish between zener breakdown and avalanche breakdown.
8. What do you understand by switching diodes?
9. Explain the capacitance of p-n junction.
10.What is Schottky barrier? Explain it by proper band diagram.
11.The p and n regions of a silicon p-n junction have resistivities of 1.0 ohm-m and
0.2 ohm-m respectively. The minority carrier lifetimes in the two regions are 5
µs and 1 µs respectively. Calculate the reverse bias saturation current density of
the p-n junction. Assume T=300 K, ni=1.5X1016 /m3 , µn=0.13 m2/V-s
andµp=0.05 m2/V-s.
12.Calculate the reverse saturation current density for the Si p-n junction with the
following parameters.
FUNDAMENTALS OF ELECTRONICS DEVICES
NEC 302
Na=Nd=5X1016 /cm3, Dn=25 cm2/s, Dp=10 cm2/s.
τ n=τp=3X10-7 s and ni=1.5X1010 /cm3 at T=300 K.
13.A Si p-n junction is made with 10 ohm-cm p-material and 0.1 ohm-cm nmaterial. Assuming that ni=1.4X1010 /cm3 at the equilibrium temperature.
Calculate the potential barrier across the junction. The electron and hole
mobility in Si is 1400 and 480 cm2/V-s respectively.
14.What do you understand by carrier injection? Derive the relevant formula.
15.Find the reverse saturation current density in an abrupt silicon junction with the
following data –
Nd=1021 /m3 , Na=1022 /m3 , Dn=3.4X10-3 m2/s , Dp=1.2X10-5 m2/s
Ln=7.1X10-4 m , Lp=3.5X10-4v m and ni=1.6X1016 /m3.
16.What do you mean by reverse recovery transient? Explain the significance of
diode reverse recovery time, storage time and transition time.
17.What are basic characteristics differences between a Schottky diode and a
conventional p-n junction diode?
FUNDAMENTALS OF ELECTRONICS DEVICES
NEC 302
ASSIGNMENT 4
1. Draw the static drain characteristics and the transfer characteristics curves for nchannels enhancement type MOSFET.
2. What is the difference between a current controlled and voltage controlled three
terminal active devices? Which is preferable?
3. What do you mean by MESFET? Explain in brief.
4. Discuss the operating principle of HEMT?
5. What is the difference between the pinch off voltage and the threshold voltage?
6. For a fixed VD explain how the drain current in an n-channel JFET is reduced as
the gate voltage is made more negative.
7. Explain why ID in a JFET remains constant with VDS in the region beyond pinch
off.
8. Give reasons why the GaAs MESFET has better high frequency response than
other transistors.
9. Derive the equation –
IC= α.IE +ICBO
Discuss the physical meaning of each variable in the above equation.
10.
a. What is common emitter gain β.
b. Draw the load line on the transistor characteristics.
11. Why?
a. Collector is wider than emitter and base
FUNDAMENTALS OF ELECTRONICS DEVICES
NEC 302
b. Base made thin.
c. Why is collector current slightly less than emitter current?
d. What are requirement of a good transistor.
12. Name the three possible transistor connections. Explain the operation of
transistor as an amplifier.
13.For an n-channel JFET IDSS=8.7 mA, VP=-3 V and VGS=-1 V. Find the value of
ID , gmo and gm.
14.Transistor is connected in common emitter configuration collector supply
voltage VCC is 10 V, load resistance RL is 800 ohm, voltage drop across load
resistance is 0.8 V and current gain α=0.96. Determine collector emitter voltage
and base current.
15.
a. What are α and β define.
b. Why FET is called voltage controlled device.
c. Comparison between JFET and MOSFET.
16.Why do we choose q point at the center of the loadline.
17. What do you meant by thermal runway?
18.Why is the transistor called a current controlled device?
19. Define current amplification factor?
20. What are the requirements for biasing circuits?
21. What are the advantages of fixed bias circuit?
22. Explain about the various regions in a transistor?
23. Explain about the characteristics of a transistor?
24.Define current amplification factor?
25. What are the requirements for biasing circuits?
ASSIGNMENT 5
1. What is photodiode? Explain the V-I characteristics of photo diode. What is the
significance of third and fourth quadrant operation of a photodiode?
2. What do you mean by optoelectric devices? How are they classified and what
are the various types of photoelectric devices?
FUNDAMENTALS OF ELECTRONICS DEVICES
NEC 302
3. Why PIN diode detector does not provide gain? How can be made more
sensitive to low level intensity of light.
4. Write a short note on materials for semiconductor lasers.
5. What is LED? Give its principle of working and its advantages and
disadvantages. Explain the direct and indirect recombination modes.
6. Describe a solar cell? Why must a solar cell be operated in the forth quadrant of
the junction V-I characteristics.
7. Define the term “population inversion”. What condition must be met for
population inversion to occur?
8. How you define hetro junctions in a typical semiconductor laser? How is it
related to the population inversion?
9. What are degenerate semiconductors?
10.Explain the phenomenon of tunneling in a highly doped p-n junction.
11.Using energy band diagram (Fermi Level) explain the tunnel-diode
characteristics (V-I curve) point by point.
12.What does the acronym IMPATT stands for? How can you say that IMPATT is
a negative conductance microwave device? Explain the principle of operation of
an IMPATT diode.
13.What is Gunn Effect or Explain the bulk transferred electron mechanism and
negative resistance as applied to Gunn Diodes.
14.What is Gunn domain? How are they formed and what is it that they do? Or
Explain domain formation in Gunn diode.
15.How does the difference in the mobility of electrons in the upper and lower
valleys give rise to the phenomenon of negative conductance?
16.Write short note on –
a. DIAC
b. IGBT
c. TRIAC
17.Explain the two transistor analogy of SCR. When this analogy not valid? Give
the necessary mathematical derivations also.
FUNDAMENTALS OF ELECTRONICS DEVICES
NEC 302