JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.16, NO.5, OCTOBER, 2016
http://dx.doi.org/10.5573/JSTS.2016.16.5.695
ISSN(Print) 1598-1657
ISSN(Online) 2233-4866
p-Type Doping of GaSb by Beryllium Grown on
GaAs (001) Substrate by Molecular Beam Epitaxy
Djalal Benyahia1,*, Łukasz Kubiszyn2, Krystian Michalczewski1, Artur Kębłowski2,
Piotr Martyniuk1, Józef Piotrowski2, and Antoni Rogalski1
Abstract—Be-doped GaSb layers were grown on
highly mismatched semi-insulating GaAs substrate
(001) with 2° offcut towards <110> at low growth
temperature, by molecular beam epitaxy (MBE). The
influence of Be doping on the crystallographic quality,
surface morphology, and electrical properties, was
assessed by X-ray diffraction, Nomarski microscopy,
and Hall effect measurements, respectively. Be
impurities are well behaved acceptors with hole
concentrations as high as 9×1017 cm-3. In addition, the
reduction of GaSb lattice parameter with Be doping
was studied.
Index Terms—Molecular beam epitaxy, GaSb, doping,
high resolution X-ray diffraction, semiconducting IIIV materials
I. INTRODUCTION
Antimonide-based semiconductors have potential
applications in a wide range of electronic and
optoelectronic devices because of their exceptional band
alignments, and small effective mass, in addition to
extremely high electron mobility [1-3]. For that reason,
there has been much attentiveness and huge progress
done in the material growth and device invention of
antimonide semiconductor heterostructures, such as field
effect transistors [4], semiconductor lasers [5], and
Manuscript received Apr. 5, 2016; accepted Jul. 3, 2016
1
Institute of Applied Physics, Military University of Technology, 2
Kaliskiego Str., 00-908 Warsaw, Poland
2
Vigo System S.A., 129/133 Poznańska Str., 05-850 Ożarów
Mazowiecki, Poland
E-mail : [email protected]
infrared detectors [6]. Although up-to-date technical
advancements have allowed high quality lattice matched
GaSb epitaxy on native substrate, GaAs substrate are
likeable for many applications. This is due to: GaAs is
low cost, has suitable thermal properties and establishes
outstanding n and p ohmic contact. Moreover,
transparency of GaAs substrates over a wide 0.9 to
~20µm spectral range enables backside illumination of
optoelectronic devices and use of monolithic optical
immersion
technology
resulting
in
dramatic
improvements of performance of these devices [7].
Nevertheless, there is a high lattice mismatch between
GaSb and GaAs substrate of 7.8%, which leads to real
problems for the growth of good devices.
Nominally undoped GaSb is p-type due to native
defects [8]. Silicon is frequently used for n-type doping
of III-V semiconductors grown by MBE. The group IV
atoms as Si, Ge, and Sn are known as amphoteric
dopants of III-V compounds; they have the possibility to
be integrated on group III lattice sites as donors, or on
group V as lattice sites as acceptors. Alternatively, the
group VI elements S, Se, and Te are used. The p-type
dopants are C, Ge, Be. This latter is often used in the
MBE growth of III-V materials. Furthermore, it is
demonstrated that the presence of dopant atoms in
epitaxial atoms changes its electrical and crystallographic
properties [9-12]. It was shown by Sankowska et al. that
the lattice constant of GaSb layer grown on GaSb
substrate decreases by the Be doping and unintentional
As dopant. It was found that the main influence on the
GaSb lattice parameter with high Be doping is the
beryllium size effect, while the As size effect is the main
influence on the GaSb lattice parameter with low Be
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DJALAL BENYAHIA et al : p-TYPE DOPING OF GASB BY BERYLLIUM GROWN ON GAAS (001) SUBSTRATE BY …
doping. Also, the change of the strain in the InAs/GaSb
superlattice by introducing the Be dopant was
demonstrated. Jenichen et al. [13] found that high density
of misfit dislocation in AlAs/GaAs Distributed Brag
Reflectors (DBRs) can be generated by Be doping. The
X-ray measurements of these structure presented a
broadening of the satellite peaks, this confirms that the
strain was changed by the presence of Be doping. This
heterostructure was doped also with carbon, but there
was no broadening of satellite peaks.
In this paper, we report on the first results of p-type
doping of GaSb by beryllium grown on GaAs substrates
by molecular beam epitaxy. The effect of Be doping on
the electrical and crystallographic properties of GaSb
epilayer grown at low growth temperature was evaluated.
II. EXPERIMENT
Be-doped GaSb layers has been grown on (001)oriented semi-insulating GaAs substrates with 2º offcut
towards <110> in a RIBER COMPACT 21-DZ solidsource molecular beam epitaxy (MBE) system. The
growth details of GaSb layers have been reported
elsewhere [14]. We have used As4 and Sb2 as group-V
elements. The substrate temperature was measured by the
manipulator thermocouple calibrated from the GaAs
deoxidization temperature. Four GaSb layers were grown
at a growth temperature of 385 ºC with Sb/Ga flux ratio
of 5: one undoped GaSb epilayer, and three Be-doped
GaSb epilayers. The Be effusion cell temperature was
700 ºC, 760 ºC and 830 ºC. The GaSb epilayers thickness
was 2µm. Beside, the growth rate was 0.6 ML/s. The
growth process was monitored by in-situ reflection highenergy electron diffraction (RHEED).
The crystallographic properties of the samples were
assessed by high-resolution X-ray diffractometer of
PANalytical X’Pert. We have used the Cu Kα1 radiation
(λ ≈ 1.5406 Å) originating from a line focus. A four
bounce, Ge (004) hybrid monochromator was utilized to
monochromatize the X-ray beam. The measurements
were made in both ω and 2θ-ω directions. Hall
measurement using Van der Pauw method was used to
evaluate electrical characteristics. This measurement has
been performed by using ECOPIA Hall effect
measurement system. This latter gives the opportunity to
measure the electrical parameters between 80K and room
(a)
(b)
Fig. 1. Be-doped GaSb layer RHEED pattern (a) (× 1) pattern,
(b) (× 3) pattern. The Be cell temperature is 830°C.
temperature by a chosen step (here, we used 5K as a
step). Having cooled to liquid Nitrogen temperature, this
system measures Hall parameters at the initial
temperature, then, it is heated to the next temperature,
and measure again, and so, until room temperature.
While surface properties were characterized by Nomarski
optical microscopy and high resolution optical
profilometry.
III. RESULTS AND DISCUSSION
When the GaSb growth started, the RHEED pattern
switched from (4×2), characteristic of GaAs layer, to
sparkling spots, which means that the growth was
changed from a two-dimensional (2D) growth to a threedimensional (3D) one. This consequence confirms that
GaSb growth is a Volmer-Weber growth mode [15]. A
clear (1×3) RHEED pattern was seen, after few minutes,
as it is shown in Fig. 1, pointing a flat surface of GaSb
layer.
Be does not seem to manifest surface segregation in
GaSb. In fact, the growth of GaSb under Sb stabilized
conditions indicates (1×3) RHEED pattern both in the
absence and in the presence of Be, which confirms the
result of Longenbach et al. [16], they found out that
dopant segregation is not a problem in GaSb.
Fig. 2 illustrates the surface morphology of Be-doped
GaSb characterized by Nomarski microscopy. Shiny
mirror-like Be-doped GaSb layers were obtained under
optimized growth temperature and Sb/Ga flux ratio for
the four samples. In addition, the same surface quality
was obtained at 250 °C to 540 °C temperature range [14].
Not mirror-like surface were acquired after the growth of
GaSb outside this range of temperature [Fig. 2(b)].
Fig. 3(a) represents the (004) diffraction curve of Be-
JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.16, NO.5, OCTOBER, 2016
(a)
697
(b)
Fig. 2. The Nomarski optical microscopy pictures with a
magnification of 1000 of 2 μm thick Be-doped GaSb layer
grown at 385 °C with Be cell temperature 700 °C (a) and
undoped GaSb layer grown at not optimized growth parameter
(b).
Fig. 4. FWHM of Be-doped GaSb epilayers and the separation
between the GaAs substrate peak and GaSb layer peak versus
Be cell temperature. All the samples have a thickness of 2 μm.
Table 1. Structural and Electrical properties of Be-doped GaSb
layers at room temperature
Be cell temp, °C
undoped
Separation, arcsec 19209.33
(a)
(b)
Fig. 3. (004) high-resolution x-ray diffraction curve of Bedoped GaSb layer in 2θ-ω direction (a) and a zoom in the GaSb
peaks (b).
doped GaSb layer in 2θ- ω direction. It can be seen that
there are two peaks: GaAs substrate peak and GaSb layer
peak. The separation, which can be noticed from Fig.
700 °C
760 °C
830 °C
19201.32
19192.68
19183.32
Lattice const, Å
6.09752
6.09734
6.09712
6.09688
Conc, cm-3
7.4 × 1016
7.7 × 1016
1.3 × 1017
9.2 × 1017
Mobility,
cm2V-1s-1
632
507
545
386
3(b), between these two peaks represents the strain
between the GaAs substrate and the GaSb layer. As
shown in Fig. 4, this separation decreases from 19201
arcsec to 19183 arcsec when the temperature of Be cell
increases from 700 °C to 830 °C (Table 1). While, the
lattice constant of doped GaSb layer decreased as the Be
cell temperature increases, as can be seen in Table 1.
This suggests that the GaSb buffer layer becomes more
strained. The present formulas have been used:
nλ = 2d sin θ
(1)
1
h2 + k 2 + l 2
=
2
d hkl
a2
(2)
where n is a positive integer, λ is the wavelength of Cu
Kα1 radiation, θ is the scattering angle, dhkl is the spacing
between two lattice plans which miller indices is (hkl),
and ‘a’ is the lattice constant of GaSb layer.
As follows from Fig. 4, the crystal quality was found
to vary enormously with respect to the Be effusion cell
temperature. The full width at half maximum (FWHM)
of GaSb peak measured in ω direction increases as the Be
doping increases. This is due to the incorporation of Be
atoms into the GaSb lattice, which affects the crystal
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DJALAL BENYAHIA et al : p-TYPE DOPING OF GASB BY BERYLLIUM GROWN ON GAAS (001) SUBSTRATE BY …
Fig. 5. The hole concentration and Be vapor pressure versus
reciprocal Be cell temperature of Be-doped GaSb temperature.
quality of the GaSb layers.
The hole concentration and mobility of undoped GaSb
layer and Be-doped GaSb layers, are shown in Table 1. It
can be seen that the undoped GaSb is unintentionally ptype doped, which is consistent with the results of
Anayama et al. [10]. When the Be cell temperature is
700 °C, the hole concentration is 7.76×1016 cm-3, which
is almost the same value as that for undoped GaSb layer
(7.43×1016 cm-3), therefore, we can consider that the
doping is too weak when the Be cell temperature is
700 °C.
The hole concentration and the Be vapor pressure as a
function of reciprocal Be cell temperature are shown in
Fig. 5. The values of p for GaSb layers range from
8×1016 cm-3 to 1×1018 cm-3. At moderate Be source
temperature, p exhibits an Arrhenius dependence on
temperature. The activation energy of beryllium is 55
meV, it has been calculated from the slope of the
characteristic ln (Na) as a function of (1/kT), where k is
Boltzmann constant and Na is the carrier concentration.
The solid line in Fig. 5 represents the Be vapor pressure,
plotted from the Eq. (3) [17]:
log p ( atm ) = 8.042 - 17020 ´ T -1 - 0.4440 ´ log T (3)
The fact that the slope of vapor pressure curve matches
well the 1/T dependence of the hole concentration is
significant and suggests that, the Be doping level is
merely proportional to the Be atoms arrival rate.
Fig. 6 shows the dependence of hole concentration on
the temperature. The hole concentration is practically
Fig. 6. The hole concentration of undoped GaSb layer and Bedoped GaSb layers versus the temperature.
Fig. 7. The hole mobility of undoped GaSb layer and Be-doped
GaSb layers versus the temperature.
constant for high doping (Be cell temperature is 830 °C).
However, for undoped GaSb and low doped GaSb, the
hole concentration decreases at low temperatures. This is
due probably to the native defects in GaSb, which have
higher ionization energy in comparison to Be atoms.
On the other hand, the hole mobility as a function of
temperature is plotted in Fig. 7. Below room temperature,
the hole mobility varies virtually as T 1.23, it increases
with decreasing temperature, until 120 K is reached, then
drops off, which is consistent with the results of Leifer et
al. [18], who found that the mobility follows in this
temperature range the T 1.5 law. Above the temperature of
the maximum (120K) in Fig. 7, The dependence between
the hole mobility and temperature is practically linear,
Leifer et al. found the hole mobility obeys T -0.87 law.
While temperature increases, phonon concentration
increases, and causes increasing scattering which lowers
JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.16, NO.5, OCTOBER, 2016
699
type conductivity over 80 to 300K temperature range.
The highest hole concentration ~ 1018 cm-3 was obtained
with a Be cell temperature at 830 °C.
ACKNOWLEDGMENTS
This paper has been completed with the financial
support of the Polish National Science Centre, Project:
UMO-2015/17/B/ST5/01753.
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Fig. 8. The electrical conductivity of undoped GaSb layer and
Be-doped GaSb layers versus the temperature.
the carrier mobility more and more at higher temperature.
Below 120K, the mobility lowering is governed by the
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[18].
Fig. 8 shows the electrical conductivity of undoped
and Be doped GaSb layers. It can be seen that the
conductivity increases as the Be cell temperature
increases. On the other hand, the conductivity has nearly
the same trend as the mobility discussed before. The
maximum of the conductivity is at 170K. For instance, a
conductivity as high as 70 S/cm has been obtained for a
Be cell temperature of 830 °C. Owing to Be doping,
carrier concentration increases, which leads to the
mitigation of the resistivity, therefore, an increasing of
the conductivity.
IV. SUMMARY AND CONCLUSIONS
Be-doped GaSb epilayers were grown on GaAs
substrates.
Hall
effect
measurement,
X-ray
diffractometry and optical microscopy were used to
evaluate the effect of Be doping on the electrical
properties, crystalographic quality and surface
characterization of Be-doped GaSb layers, respectively.
The crystalline quality degrades when the Be doping
level increases. Beside, the strain increases between
GaSb layer and GaAs substrate. Moreover, GaSb lattice
constant decreases when the Be doping increases due to
Be size effect.
The undoped and Be-doped GaSb epilayers exhibit p-
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Djalal Benyahia was born in Mila,
Algeria, on 1989. He received the
B.S., degree in the Polytechnic
Military School, Algiers, Algeria in
2013, and M.S., degree in telecommunication in the Military University of
Technology, Warsaw, Poland, in 2015.
His research interests the growth and characterization of
the group III-V semiconductors, bulk materials, type-II
superlattices (InAs/GaSb), and infrared detectors by
molecular beam epitaxy.
Łukasz Kubiszyn was born in
Rzeszów, Poland, on 1990. He
received M.S. degree in Warsaw
University
of
Technology
in
technical physics in 2014. He joined
at Vigo System S.A., where he has
been working in the area of the
growth and investigation of group III-V materials,
including: bulk materials, type-II superlattices and
infrared detectors.
Krystian Michalczewski is a
researcher at the Institute of Applied
Physics, Military University of
Technology (MUT) in Warsaw,
Poland. He received the M.S. degree
in chemical technology from the
Department of Chemistry, Warsaw
University of Technology in 2015. His specialization is
the growth of group III-V semiconductors, bulk materials,
type-II superlattices (InAs/GaSb), wet etching and
passivation.
JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.16, NO.5, OCTOBER, 2016
Artur Kębłowski was born in
Warsaw, Poland, on 1983. He
received M.S. degree in automation
and robotics from the Faculty of
Production Engineering, Warsaw
University of Technology, in 2008.
Since 2014, he is the head of the
Epitaxy Laboratory in VIGO System S.A. His research
interests the morphology of CdTe deposited onto GaAs
substrate, engineering of the chemical vapor deposition
of HgCdTe material.
Piotr Martyniuk is an assistant
professor at the Institute of Applied
Physics, Military University of
Technology (MUT) in Warsaw,
Poland. He received the M.S. degree
in technical physics at MUT (2001),
PhD in electronics at Warsaw
University of Technology (2008), Poland and D.S. in
electronics in MUT (2015). He is currently the head of
the Institute of Applied Physics at MUT. The main
subject of his investigation is HgCdTe, InAsSb and
T2SLs IR detectors.
701
Józef Piotrowski is a researcher and
development manager at Vigo
System S.A., Warsaw, Poland, and a
scientific advisor at the Military
Institute of Armament Technology,
Zielonka. Prof. Piotrowski proposed
numerous concepts and practical
solutions related to uncooled detection. He developed
more advanced IR devices (Dember, magnetoconcentration, and photovoltaic) based on HgCdTe and other
material systems (HgZnTe, HgMnTe, InAsSb, InGaAs).
has
made
Antoni
Rogalski
pioneering contributions in theory,
design, and technology of different
types of IR detector. He is currently
an ordinary member at PAN (Polish
Academy of Sciences), and a Professor with the Institute of Applied
Physics, Military University of Technology, Warsaw,
Poland. Prof. Rogalski is an active member of the
international Technical Community. He is a Chair and
Co-Chair, an Organizer, and a member of Scientific
Committees of many national and international
conferences on optoelectronic devices and material
science.