Solid state doping of CdxHg₁₋xTe epitaxial layers with elements of V group
Presented here are the results of studying the controlled doping with elements of V group of the periodic table, arsenic As and antimony Sb, of narrow gap CdxHg₁₋xTe epitaxial layers during the isothermal growth from the vapour phase by the evaporation-condensation-diffusion method. Three types of i...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2006
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| Цитувати: | Solid state doping of CdxHg₁₋xTe epitaxial layers with elements of V group / A.P. Vlasov, A.Yu. Bonchyk, I.M. Fodchuk, R.A. Zaplitnyy, A. Barcz, Z.T. Swiatek // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 1. — С. 36-42. — Бібліогр.: 15 назв. — англ. |
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irk-123456789-1215912017-06-15T03:03:56Z Solid state doping of CdxHg₁₋xTe epitaxial layers with elements of V group Vlasov, A.P. Bonchyk, A.Yu. Fodchuk, I.M. Barcz, A. Swiatek, Z.T. Zaplitnyy, R.A. Presented here are the results of studying the controlled doping with elements of V group of the periodic table, arsenic As and antimony Sb, of narrow gap CdxHg₁₋xTe epitaxial layers during the isothermal growth from the vapour phase by the evaporation-condensation-diffusion method. Three types of impurity sources have been used for solid state doping: homogeneously doped with As(Sb) single crystal substrates of CdTe, As doped buffer CdyHg₁₋yTe (y > x) epitaxial layers obtained by RF sputtering in mercury glow discharge onto undoped CdTe substrates, and As(Sb) implanted undoped CdTe substrates. The results of comparative analysis of galvano-magnetic measurements and SIMS spectra indicated very high, practically nearly ~100 %, electrical activity of dopants in the CdxHg₁₋xTe epitaxially grown layers. 2006 Article Solid state doping of CdxHg₁₋xTe epitaxial layers with elements of V group / A.P. Vlasov, A.Yu. Bonchyk, I.M. Fodchuk, R.A. Zaplitnyy, A. Barcz, Z.T. Swiatek // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 1. — С. 36-42. — Бібліогр.: 15 назв. — англ. 1560-8034 PACS 61.72.V; 72.80.E http://dspace.nbuv.gov.ua/handle/123456789/121591 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Presented here are the results of studying the controlled doping with elements of V group of the periodic table, arsenic As and antimony Sb, of narrow gap CdxHg₁₋xTe epitaxial layers during the isothermal growth from the vapour phase by the evaporation-condensation-diffusion method. Three types of impurity sources have been used for solid state doping: homogeneously doped with As(Sb) single crystal substrates of CdTe, As doped buffer CdyHg₁₋yTe (y > x) epitaxial layers obtained by RF sputtering in mercury glow discharge onto undoped CdTe substrates, and As(Sb) implanted undoped CdTe substrates. The results of comparative analysis of galvano-magnetic measurements and SIMS spectra indicated very high, practically nearly ~100 %, electrical activity of dopants in the CdxHg₁₋xTe epitaxially grown layers. |
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Vlasov, A.P. Bonchyk, A.Yu. Fodchuk, I.M. Barcz, A. Swiatek, Z.T. Zaplitnyy, R.A. |
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Vlasov, A.P. Bonchyk, A.Yu. Fodchuk, I.M. Barcz, A. Swiatek, Z.T. Zaplitnyy, R.A. Solid state doping of CdxHg₁₋xTe epitaxial layers with elements of V group Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Vlasov, A.P. Bonchyk, A.Yu. Fodchuk, I.M. Barcz, A. Swiatek, Z.T. Zaplitnyy, R.A. |
| author_sort |
Vlasov, A.P. |
| title |
Solid state doping of CdxHg₁₋xTe epitaxial layers with elements of V group |
| title_short |
Solid state doping of CdxHg₁₋xTe epitaxial layers with elements of V group |
| title_full |
Solid state doping of CdxHg₁₋xTe epitaxial layers with elements of V group |
| title_fullStr |
Solid state doping of CdxHg₁₋xTe epitaxial layers with elements of V group |
| title_full_unstemmed |
Solid state doping of CdxHg₁₋xTe epitaxial layers with elements of V group |
| title_sort |
solid state doping of cdxhg₁₋xte epitaxial layers with elements of v group |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2006 |
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http://dspace.nbuv.gov.ua/handle/123456789/121591 |
| citation_txt |
Solid state doping of CdxHg₁₋xTe epitaxial layers with elements of V group / A.P. Vlasov, A.Yu. Bonchyk, I.M. Fodchuk, R.A. Zaplitnyy, A. Barcz, Z.T. Swiatek // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 1. — С. 36-42. — Бібліогр.: 15 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 36-42.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
36
PACS 61.72.V; 72.80.E
Solid state doping of CdxHg1-xTe epitaxial layers
with elements of V group
A.P. Vlasov1, O.Yu. Bonchyk2, I.M. Fodchuk3, R.A. Zaplitnyy3, A. Barcz4, Z.T. Swiatek5
1I. Franko Lviv National University, 1, Universitetska str., 79000 Lviv, Ukraine
2Institute for Applied Problems of Mechanics and Mathematics, NAS of Ukraine
3-b, Naukova str., 79601 Lviv, Ukraine
3Yu. Fed’kovich Chernivtsi National University, 19, Universitetska str., 58012 Chernivtsi, Ukraine
4Institute of Physics of Polish Academy of Sciences, 32/46 Al. Lotnikow, 02-668 Warsaw, Poland
5Institute of Metallurgy and Materials Science, Polish Academy of Science
25 Reymonta Str., 30-059 Krakow, Poland
Abstract. Presented here are the results of studying the controlled doping with elements
of V group of the periodic table, arsenic As and antimony Sb, of narrow gap CdxHg1−xTe
epitaxial layers during the isothermal growth from the vapour phase by the evaporation-
condensation-diffusion method. Three types of impurity sources have been used for solid
state doping: homogeneously doped with As(Sb) single crystal substrates of CdTe, As
doped buffer CdyHg1−yTe (y > x) epitaxial layers obtained by RF sputtering in mercury
glow discharge onto undoped CdTe substrates, and As(Sb) implanted undoped CdTe
substrates. The results of comparative analysis of galvano-magnetic measurements and
SIMS spectra indicated very high, practically nearly ~100 %, electrical activity of
dopants in the CdxHg1−xTe epitaxially grown layers.
Keywords: X-ray spectrometry, substrate, epitaxial layer.
Manuscript received 30.10.05; accepted for publication 15.12.05.
1. Introduction
The narrow-gap solid solutions of cadmium and mercury
tellurides – CdxHg1−xTe (x = 0.18…0.3) are the most
suitable semiconductor materials for producing high
efficient detectors of infra-red radiation (IR) for 3 to 5 and
8 to 14 μm atmospheric windows [1]. In spite of the
technological difficulties, high production cost and
development of investigation of alternative materials, there
exists the necessity to improve the methods of obtaining
both CdxHg1−xTe itself and detectors based on it. When
producing the photovoltaic detectors on the basis of
CdxHg1−xTe epitaxial heterostructures, great efforts are
being directed on obtaining a doped material with
required electrophysical properties. The element of V
group As is considered to be the most attractive acceptor
impurity in CdxHg1−xTe, since 100 % activation of
acceptor states in the material may be reached at the
concentration of 5⋅1018 сm−3. Nevertheless, such
activation levels have been achieved at liquid-phase
epitaxy from melts enriched with Hg. The doped epitaxial
layers of CdxHg1−xTe obtained by molecular-beam epitaxy
possess a n-type of conductivity after the growth, and to
achieve high-level activation of the acceptor impurity, an
additional annealing in Hg vapour is used [2]. Therefore,
understanding of an amphoteric nature of the impurity
and possibility to control the process of impurity
incorporation in CdxHg1−xTe are necessary for obtaining
the material suitable to produce high-quality photovoltaic
structures.
The aim of this paper was to investigate the
processes of autodoping with the acceptor impurity As
(Sb) of CdxHg1−xTe epitaxial layers at isothermal vapour
phase growth by the method of evaporation-condensation-
diffusion (ECD).
2. Experimental techniques
During the EVC epitaxial growth of CdxHg1−xTe layers,
we used the substrates with three types of impurity
sources:
I. Homogeneously doped single crystals of CdTe grown
by the Bridgmann method with impurity incorporated
during the synthesis process at the concentration level of
NAs~1016…1017cm−3 (NSb~1017…1018cm−3).
II. Undoped CdTe (111) and CdTe (110) crystals on surfa-
ces of which heavily doped with As (NAs~1019…1020 cm−3)
epitaxial buffer films of CdyHg1−yTe were deposited.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 36-42.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
37
III. Undoped CdTe (111) and CdTe (110) crystals on
surfaces of which controlled amount of As (Sb) was
incorporated by ion implantation.
The surface sources of dopant of II type were
produced by RF (f = 13.56 MHz) sputtering in mercury
glow discharge of wider gap (y > x) CdyHg1−yTe epitaxial
buffer films (y denotes the composition of a solid solution
film with a dopant, whereas x denotes the composition
at the surface of CdxHg1−xTe graded-gap epitaxial
layers). To introduce As with concentrations greater than
1 at.%, the sputtering of the pure element along with the
target material was carried out. For obtaining the
concentration less than 0.01 at.% the impurity was
introduced during the target synthesis using the weight of
As. The contents of impurity in the film were controlled
by the area from which the sputtering took place. When
using the source of ІІІ type As(Sb) impurity was
implanted with the equal ion energy Е = 100 keV.
Inhomogeneity of the dopant doze did not exceed 1 %,
reproducibility was 98 %.
For implementation of the vapour-phase epitaxy [3],
we used silica ampoules and accessory. Flatness and
mirror-like surfaces of CdTe substrates were achieved
by means of an abrasive-free chemico-mechanical
polishing in a bromine-butanol etchant. The mounted
ampoules were evacuated by oil-free pumping down to a
residual pressure of ~10−4 Pa, afterwards they were
sealed and weighted in a two-zone furnace with resistive
heating. In all experiments the temperature of growth
zone amounted to 600 °С. The temperature of the other
zone was maintained at the level that provided the
pressure of the saturated mercury vapour during the
epitaxial growth equal to РHg = (2…4)⋅105 Pa. In order to
increase the number of mercury vacancies created at the
final stage of CdxHg1−xTe epitaxy, an annealing in the
isothermal regime in mercury vapour at the temperature
320 °С was carried out for 60 hours. At these regimes of
growth and post-growth annealing undoped epitaxial
layers of CdxHg1−xTe had n-type of conductivity.
Diagnostics of the structural changes in the near-
surface regions of single crystals and epitaxial layers of
CdxHg1−xTe was performed using the Х-ray methods
since they are non-destructive and highly sensitive to
various types of distortions of atomic planes. For the
research, the Berg-Barrett method in asymmetric and
skew-symmetric geometry of backward diffraction was
used [4, 5]. For obtaining the rocking curves (RC), we
used the method of two-crystal spectrometer in a
dispersionless scheme (n,−n). The skew-asymmetric
scheme of X-ray diffraction makes it possible to
investigate selectively and layer-by-layer with a step of
∼0.05 μm and less the structural changes in the near-
surface layers after the influence of different external
factors, for example, ion implantation. By azimuth
rotation of a crystal around the diffraction vector by the
angle ψ, one can realize the case when the penetration
depth of X-rays would be of the same order as the depth
of the disturbed by ions near-surface layers
h
h
L γγ
χ
λ
0ext = , (1)
where
ψθψϕθγ cossinsincoscos
,0
±−=
h
, (2)
hh ,0,0
sinφγ = , (3)
where φ0,h are the incidence and exit angles of Х-rays,
θ is the diffraction angle, ψ is the disorientation angle
between the planes of incidence and reflection, Lext is the
extinction length, χh are the coefficients of Fourier-
polarization, λ is the wavelength, the sign "plus"
corresponds to the incident and "minus" – to the
diffracted ray.
Table shows the galvanomagnetic properties of
CdxHg1-xTe samples investigated by the standard
technique of Hall measurements at Т = 77…300 К and
the magnetic fields ranging from 0.005 to 1.7 T. The
composition of CdxHg1−xTe epitaxial layers was
controlled using the spectra of optical absorption.The
distribution of impurity concentration and the profiles of
composition of CdxHg1−xTe epitaxial layers were deter-
mined by the Secondary Ion Mass-Spectrography (SIMS)
at Cameca IMS-6F device. Simultaneously the analysis
of the impurity and the main component isotope of
CdxHg1−xTe (202Hg 130Te or 202Hg 133Cs) has been carried
out. The sensitivity limit of the device for the analyzed
impurities was in the range from 5⋅1014 to 1015 cm−3.
The quantitative composition of the main
components along the thickness of the grown epitaxial
CdxHg1−xTe layer was determined from X-ray
microanalysis spectra. Measurements of the spectra
were performed on the sample cross cleavages by
means of a Scanning Electron Microscope based on
microanalyser JXA-50A (JEOL). The composition
measurement error did not exceed 1%.
3. Results of researches
The CdxHg1-xTe epitaxial layers grown on the As
homogeneously doped substrates of CdTe had the hole
type of conductivity. The boundary of maximum
penetration of Hg in the CdTe substrate is clearly seen
in the SEM-microphotography of the cross cleavage of
typical sample 73-2 grown on the CdTe substrate with
NAs ~ 1016 cm−3 (Fig. 1a). The composition-distribution
curve measured with the help of X-ray microanalysis
for the As doped epitaxial layer (Fig. 1a) does not differ
from the typical composition profiles in CdxHg1−xTe
samples obtained during the epitaxy on undoped CdTe
substrates with the analogous growth regimes. Fig. 1a
also shows the SIMS distribution along the depth of
CdxHg1−xTe epitaxial layer. The acceptor concentration
determined in this sample by means of galvanomagnetic
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 36-42.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
38
Table. Results of electrophysical investigation of doped with As (Sb) ECD epitaxial layers of CdxHg1–xTe.
No Sample
number
Dopant source x d, μm μ , cm2/(V·s) RH, cm3/Q Na – Nd, cm–3
77 К
273 К 77 К 273 К 77 К
1 V-23 Undoped 0.23 64 7740 20050 −610 −1480 4.2·1015
As
2 73-2 Substrate 0.213 57 3741 150 −293 +464 1.35·1016
3 770-V32 Buffer film – 59 54 52 +16 +37 1.7·1017
4 771-V33 Buffer film – 62 150 43 −91 +56 1.12·1017
5 77-2(110) Implanted impurity 0.241 67 5850 329 −562 +518 1.2·1016
Sb
6 80-5(Sb) Substrate 0.19 70 10370 245 –200 +198 3.17·1016
7 80-6(Sb) Substrate 0.24 80 11780 387 –268 +160 3.3·1016
measurements (Fig. 1b) corresponds to the real As
concentration in the epitaxial layer and signifies the high
(close to 100 %) level of the electrical activity of the
impurity.
The successful use of the above described CdTe
substrates for obtaining CdxHg1−xTe epitaxial layers
incites the search of the alternative methods of the
dopant source production. Figs 2a and 2b schematically
show the structures with the impurity sources which are
formed on the surface of undoped CdTe single crystals
used as substrates for ECD epitaxy. Below, the results of
the fulfilled investigation using such sources are
presented.
When doping the CdxHg1−xTe ECD epitaxial layers
by using the structures shown in Fig. 2a, the identical
technological regimes for deposition of As highly
doped films in samples 770 and 771 have been used.
CdTe undoped single crystals with the (111) and (110)
surface orientations were used.
The film thickness of the sample 770 was 6.5 μm and
the estimated impurity concentration by the target doping
level was estimated to be NAs~1019 сm−3, and for the
sample 771 – 5 μm and NAs~1020 cm−3, correspondingly.
These heterostructures were applied for As doping of
the CdxHg1−xTe ECD epitaxial layers – samples 770-V32
and 771-V33 (Table). The initial position of the impurity
source in the buffer film is shown by rectangles on the
corresponding SIMS plofiles (Fig. 3): the base corresponds
to the film thickness, the height – to the impurity
concentration in the target. After the completion of the
epitaxy process in the sample 770-V32 (Fig. 3a), total
smoothing of the As profile along the structure thickness
has occurred, whereas in the sample 771-V33 (Fig. 3b)
the source did not completely exhaust itself. The
maximum residual concentration of As in the buffer film
of the sample 771-V33 corresponds to the calculated
concentration of dopants in the target. This is a
confirmation of the effective incorporation of the impurity
into CdyHg1−yTe films during the low temperature epitaxy
in Hg glow discharge and, respectively, ensures the high
efficiency of As doping for CdxHg1−xTe layers when used
during ECD epitaxy [6].
a
b
Fig. 1. a) SEM microphotography of the cross cleavage of
sample 73-2 with the profile of composition distribution and
SIMS distribution of As along the depth of Cd0.21Hg0.79Te
epitaxial layer; b) magnetofield dependences of the Hall
coefficient and conductivity for the sample 73-2.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 36-42.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
39
a
b
Fig. 2. Structure of substrates with surface impurity sources used
at doping of CdxHg1−xTe epitaxial layers. Impurity source on
CdTe undoped single crystal substrates: a) highly doped with
the As wider gap (y > x) CdyHg1−yTe epitaxial film; b) surface
layer of a substrate implanted with As (Sb) ions.
When using the As(Sb) ion implanted impurity source,
the structures based on CdTe (Fig. 2b) were mounted
immediately after the ion implantation without any
additional chemical processing in silica ampoules and were
loaded into furnaces for carrying out the ECD epitaxy
process [7]. The grown layers had mirror-like surfaces.
At the initial stages of the epitaxial growth, the state of a
substrate crystal structure is of paramount importance. For
establishing the influence of the disturbed surface layer on
the ECD epitaxy, we have carried out X-ray study of both
CdTe substrates after ion implantation and CdxHg1−xTe
doped epitaxial layers grown on them [8].
During the implantation of As ions, in the near
surface regions of CdTe single crystal, the disorder and
damages consisting of considerable concentration of
intrinsic defects in two sublattices, cluster formations,
as well as surface dislocations and stacking faults
originate [9]. The set of these imperfections causes the
creation of strained regions in the surface layers of a crystal,
which is correspondingly reflected in the X-ray topograms
and swing curves. Fig. 4 shows the most typical topograms
of the CdTe single crystal surface obtained in the
asymmetric (Fig. 4a) and skew-asymmetric (Fig. 4b)
diffraction schemes. A peculiarity of the studied sample
lies in the fact that in CdTe substrate prepared by the
standard procedure As ions are implanted only into the
half of its surface. In the implanted part (A) of the
crystal, in contrast to the non-implanted one (B), there
takes place a distortion and tailing (331) of the reflexes
of the CuKα1,2 line doublet. The reason for this is both the
bulk disturbances of crystal perfection – the availability
of the fragment structure or low-angle boundaries
(Fig. 4a) and the gradient of the lattice parameter in
certain crystallographic directions on the crystal surface.
At azimuth rotation of a crystal around the diffraction
vector, the tailings and mergings of the diffraction
maxima are observed in the topograms. During the
penetration of X-rays at the depth Lext ∼ 0.35 μm, the part
of the crystal no longer diffracts X-rays (Fig. 4b). Such a
picture is caused by the great disorder of the crystal lattice in
the subsurface layers at the depth up to 0.35 μm and gives
rise to the strains at the interface between surface layer
and implant on one side and CdTe crystal on the other.
The swing curves obtained from the As implanted
crystal parts (Fig. 5a) are characterized by an increase in the
curve shape asymmetry and the magnitudes of its half-width
(approximately by 2 to 2.5 times). The small decay in
amplitude oscillations is observed near the main maximum
of the intensity. This is mainly caused by the presence of the
gradient of lattice distance along the crystal normal in the
implanted region. Such gradient changes in the lattice
parameter amount up to 1.1⋅10−4…2.3⋅10−4 Å.
a
b
Fig. 3. SIMS distribution of the As concentration and 202Hg133Cs
signal along the thickness of CdxHg1−xTe ECD epitaxial layers
grown on undoped epitaxial buffer films of CdyHg1−yTe. For the
sample 770-V32: NAs ~ 1019 cm–3, CdTe (111) (a), 771-V33:
NAs ~ 1020 cm–3, CdTe (110) (b).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 36-42.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
40
a
b
Fig. 4. X-ray topogram of CdTe single crystal. CuKα-radiation,
(111) surface of incidence: asymmetric scheme of diffraction,
(331) reflection, ×18, Lext = 2.6 μm (a), skew-asymmetric
scheme, (511) reflection, ×18, Lext = 0.35 μm (b). Mechanical
damages – (1), interface between doped and undoped regions –
(2), inclusions (minimal size – 60-90 μm, maximal size –
300 μm) – (3).
Using the numerical method of RC modeling based on
semikinematic approximation of the X-ray scattering, the
thickness of the disturbed layer on CdTe surface after As
ion implantation (Е = 100 keV; D = 1·1015 cm−2) has been
determined [8, 9]. The region of the large disorder lies in the
range of ~0.3…0.35 μm and the total region of marked
structural disturbance extends to the depth of
~0.6…0.8 μm from the surface.
To determine the depth distribution of strains in the
near surface layer, we have used approaches based of the
basic principles of the dynamic theory of the X-ray
scattering – numerical solutions of the Takagi
differential equation system and comparison of the
obtained results with the experimental data [10]. The
calculated profile of deformation and corresponding SIMS
profile of the impurity distribution in the near surface
region of CdTe single crystal after As implantation are
demonstrated in Fig. 5b.
The Cd0.24Hg0.76Te epitaxial layer of the sample 77-2
(Table) was grown on CdTe (110) substrate in which As
ions with the dose D = 1015 cm−2 had been implanted.
The characteristic form of the thickness dependence of
the impurity concentration in the grown layer in the
sample 77-2 (Fig. 6a) is slightly different for the
epitaxial layers grown on the implanted surface of CdTe
(111) undoped substrates. Fig. 6b shows the
magnetofield dependences of the Hall coefficient and
conductivity of this sample at Т = 77 К, which indicates
the high level of electrical activity of the impurity in the
obtained epitaxial layer.
a
b
Fig. 5. Rocking curves of diffraction reflection of CdTe single
crystal. CuKα-radiation, symmetric scheme of diffraction,
(111) incidence, (333) reflection (a). Profiles of deformation
and impurity distribution in the near surface region of СdTe
(111) crystal after As implantation (b).
It follows from the analysis of X-ray structural data
(Fig. 7) that the grown layers are perfect – in the
topograms (Fig. 7a) a clear separation of the Кα-doublet
lines is seen. At the same time, there are local regions that do
not diffract X-rays, with a density of ≈103 cm-2 and
dimensions of 50–100 μm, among them tellurium
inclusions are possible. The RC intensity distribution
shown in Fig. 7b has a characteristic Gaussian form. The
half-width of the rocking curves for the sample 77-2 is in
the range of 70'' to 80''. This is indicative of the fact that
annihilation of radiation defects and recrystallization of
the disordered near surface layers in CdTe substrate
occur at the initial stages of ECD epitaxy and do not
result in deterioration of the crystal structure in
CdxHg1−xTe doped epitaxial layers.
The high efficiency of doping from the As solid state
source during the ECD epitaxial growth [7] has given an
incitement to use another element of V group, Sb, as an
impurity. Its successful usage for the liquid phase
epitaxial layers of Cd0.22Hg0.78Te has been shown by the
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 36-42.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
41
authors of the paper [13]. The choice of antimony is
caused by the following reason. Impurities of V group (Р,
Аs) in CdTe crystals are shallow acceptors [14]. This
provides comparatively high conductivity of this material,
and Sb doping provides the possibility of obtaining
semiisolating material where the conductivity is controlled
by deep acceptors with energy separated levels [15]. The
latter is attractive from the viewpoint of improving the
electrophysical properties of CdxHg1−xTe epitaxial layers.
This takes place due to the reduction of the influence of
transition regions epitaxial layer – substrate on these
properties.
We used the homogeneously Sb doped CdTe single
crystals (NSb ~ 1017 cm-3) and the structures shown in Fig. 2b
as substrates for epitaxial growth of CdxHg1−xTe by the
ECD method. Table lists the resulting electrophysical
properties of the CdxHg1−xTe ECD epitaxial layers of
samples 80-5 and 80-6. In both cases, we can observe
that, during the epitaxy, similarly to As doping, there
occurs uniform doping of the grown graded-gap layer of
CdxHg1−xTe with Sb, and the carrier concentration
correlates with the Sb concentration determined by the
SIMS technique.
a
b
Fig. 6. SIMS distribution of As and 202Hg133Cs signal along the
thickness of CdxHg1−xTe ECD epitaxial layer of the sample 77-2
(a); magnetofield dependences of the Hall coefficient and
conductivity (b).
a
b
Fig. 7. Topogram of the sample 77-2. CuKα-radiation, (111)
surface of incidence: symmetric scheme of diffraction, (333)
reflection, ×18, Lext = 7.6 μm (a); rocking curve of the sample
77-2 (b).
a
b
Fig. 8. SEM microphotograph of cross cleavage of the sample
92-4 with the profile of composition distribution and SIMS
distribution of Sb along the thickness of CdxHg1−xTe epitaxial
layer (a); topogram of the sample 92-4: CuKα-radiation, skew-
asymmetric scheme of diffraction: (111) plane of incidence,
(511) reflection – ϕ = 90°, Ф0=29°, Lext = 1.01 μm (b).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 36-42.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
42
For example, Fig. 8a illustrates the typical SEM
microphotography of the cross cleavage with the shown
distribution profiles of both the impurity and composition
measured using the X-ray microanalyser for the sample
92-4, where the implanted with Sb undoped CdTe surface
was used as a dopant source (Е = 100 keV,
D = 8⋅1014 cm−2).
For the study of quality of the grown epitaxial layers,
we have carried out X-ray topographical investigation.
Fig. 8b shows the topogram of the sample 92-4 where
the lines of Kα-series are separated without broadening
and distortion. This allows one to conclude that grown
CdxHg1−xTe epitaxial layers doped with Sb are uniform
and structurally perfect.
4. Conclusions
CdxHg1−xTe epitaxial layers with close to 100 % level of
electrical activity of the impurities have been obtained
using doping with arsenic (antimony) during isothermal
vapour phase epitaxy.
Investigation of the peculiarities of ion
implantation of the epitaxial layers allows to obtain
information concerning the behaviour of physical
processes and establish the mechanisms responsible
for changes in the defect sub-system of CdxHg1−xTe
epitaxial layers.
The structural defects in disordered regions of
radiation damages, which are created during the As (Sb)
implantation with an energy of 100 keV in the near
surface layers of CdTe single crystal substrates at
irradiation doses of D < 5⋅1015 cm–2, annihilate at the
initial stages of epitaxy and virtually do not influence the
structural perfection of the grown CdxHg1−xTe epitaxial
layers.
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