Growing the high-resistive Cd₁₋xZnxTe single crystals from a vapor phase
A modified vapor phase growth method to obtain high-resistive Cd1-xZnxTe single crystals (0 < x < 0.13) is presented. The single crystals (about 25 cm⁻³ in size) with natural faceting were grown by vapor transport in silica ampoules with a special shape using a polycrystalline ingot as i...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
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irk-123456789-1218622017-06-20T03:02:24Z Growing the high-resistive Cd₁₋xZnxTe single crystals from a vapor phase Feychuk, P. Kopyl, O. Pavlovich, I. Shcherbak, L. A modified vapor phase growth method to obtain high-resistive Cd1-xZnxTe single crystals (0 < x < 0.13) is presented. The single crystals (about 25 cm⁻³ in size) with natural faceting were grown by vapor transport in silica ampoules with a special shape using a polycrystalline ingot as initial source material. It is shown that minimization of plastic deformation effect in preparation of the most structurally perfect crystals is possible by a way of heat removal from the crystallization front by radiation. The growth of high-resistive material required careful preparation of the initial charge with close to stoichiometric composition. The obtained crystals were successfully tested for creating the room temperature X-ray and gamma-ray detectors. 2005 Article Growing the high-resistive Cd₁₋xZnxTe single crystals from a vapor phase / P. Feychuk, O. Kopyl, I. Pavlovich, L. Shcherbak // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2005. — Т. 8, № 1. — С. 110-113. — Бібліогр.: 15 назв. — англ. 1560-8034 PACS: 61.72y, 81.05, Dz; 81.10.Bk http://dspace.nbuv.gov.ua/handle/123456789/121862 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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A modified vapor phase growth method to obtain high-resistive Cd1-xZnxTe
single crystals (0 < x < 0.13) is presented. The single crystals (about 25 cm⁻³ in size)
with natural faceting were grown by vapor transport in silica ampoules with a special
shape using a polycrystalline ingot as initial source material. It is shown that
minimization of plastic deformation effect in preparation of the most structurally
perfect crystals is possible by a way of heat removal from the crystallization front by
radiation. The growth of high-resistive material required careful preparation of the
initial charge with close to stoichiometric composition. The obtained crystals were
successfully tested for creating the room temperature X-ray and gamma-ray detectors. |
| format |
Article |
| author |
Feychuk, P. Kopyl, O. Pavlovich, I. Shcherbak, L. |
| spellingShingle |
Feychuk, P. Kopyl, O. Pavlovich, I. Shcherbak, L. Growing the high-resistive Cd₁₋xZnxTe single crystals from a vapor phase Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Feychuk, P. Kopyl, O. Pavlovich, I. Shcherbak, L. |
| author_sort |
Feychuk, P. |
| title |
Growing the high-resistive Cd₁₋xZnxTe single crystals from a vapor phase |
| title_short |
Growing the high-resistive Cd₁₋xZnxTe single crystals from a vapor phase |
| title_full |
Growing the high-resistive Cd₁₋xZnxTe single crystals from a vapor phase |
| title_fullStr |
Growing the high-resistive Cd₁₋xZnxTe single crystals from a vapor phase |
| title_full_unstemmed |
Growing the high-resistive Cd₁₋xZnxTe single crystals from a vapor phase |
| title_sort |
growing the high-resistive cd₁₋xznxte single crystals from a vapor phase |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2005 |
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http://dspace.nbuv.gov.ua/handle/123456789/121862 |
| citation_txt |
Growing the high-resistive Cd₁₋xZnxTe single crystals from a vapor phase / P. Feychuk, O. Kopyl, I. Pavlovich, L. Shcherbak // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2005. — Т. 8, № 1. — С. 110-113. — Бібліогр.: 15 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
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2025-07-08T20:41:30Z |
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2005. V. 8, N 1. P. 110-113.
PACS: 61.72y, 81.05, Dz; 81.10.Bk
Cd1–xZnxTe high-resistive single crystals growth
from a vapor phase
P. Feychuk1, O. Kopyl2, I. Pavlovich2, L. Shcherbak1
1 Chernivtsi National University, 2, Kotsyubinsky str., 58012 Chernivtsi, Ukraine
E-mail: feychuk@chnu.cv.ua
2 Institute of Thermoelectricity, P. O. Box 86, 58002 Chernivtsi, Ukraine
Abstract. A modified vapor phase growth method to obtain high-resistive Cd1-xZnxTe
single crystals (0 < x < 0.13) is presented. The single crystals (about 25 cm–3 in size)
with natural faceting were grown by vapor transport in silica ampoules with a special
shape using a polycrystalline ingot as initial source material. It is shown that
minimization of plastic deformation effect in preparation of the most structurally
perfect crystals is possible by a way of heat removal from the crystallization front by
radiation. The growth of high-resistive material required careful preparation of the
initial charge with close to stoichiometric composition. The obtained crystals were
successfully tested for creating the room temperature X-ray and gamma-ray detectors.
Keywords: CdTe, Cd1–xZnxTe, vapor crystal growth, high resistivity, gamma-ray
detectors.
Manuscript received 17.12.04; accepted for publication 18.05.05.
1. Introduction
Both CdTe and Cd1–xZnxTe single crystals are known as
very good materials for room temperature gamma- and
X-ray detectors [1, 2] and have many various
applications in optoelectronics (IR-devices,
photorefractive materials, solar cells, etc). For this
purpose, the crystals with low density of linear and bulk
structure defects (dislocations, grain boundaries,
inclusions, and precipitates) are desirable in the most
cases. Cd1–xZnxTe bulk crystals are grown from the melt
usually. Zn presence causes the rises of the melt
crystallization temperatures and makes the crystals
growth from the liquid phase more complicated,
especially at high x. Besides, for the application in the
gamma-ray detectors, it is necessary to use high-resistive
material with a high μτ-product, which is reached
usually by doping (In or Cl) only. In this connection,
comparatively low temperatures during vapor growth
have attracted increasing interest of researches [3 – 5].
Vapor growth methods can be divided by three main
directions according to degree of a growing crystal
interaction with container and vapor flows [3 – 10]:
• single crystal growth on a seed or a quartz container
bottom with final completing of the container cross-
section [5 – 7];
• free growth without contact with the container walls
(free-contact growth on a quartz or single crystal
pedestal) [3, 8];
• growth on broken [4] or previously formed ingot [9, 10].
Second method requires to use ampoules of rather
complex construction in the solid solution crystals
growth case. Composition and structure of the obtained
crystals are inhomogeneous along the ingot due to a
difference between temperatures of the starting charge
and condensed material behind the crystal [11].
In [12], it was concluded that there are dislocations
and small-angle grain boundaries generated at the
interface in heterogeneous nucleation on the quartz
container walls mostly due to mechanical stresses. The
last are caused by mismatch between thermal expansion
coefficients of the container and the crystal even at slight
temperature variations (∼ 0.1 K). Estimations [12] show
that about 103 cm–2 dislocations can be generated during
one variation cycle.
The aim of this paper is to eliminate advantages and
disadvantages of the third method of the solid solution
growth, namely, the modified method of Lo et al. [10]
using polycrystalline compounds as the source material.
The results obtained by researchers upon the possibility
to grow the high-resistive Cd1–xZnxTe (0 < x < 0.13)
single crystals with natural faceting on polycrystalline
charge and their conceivable applications are discussed.
2. Experimental procedure
Polycrystalline charges Cd0.96Zn0.04Te1±δ and
Cd0.87Zn0.13Te1±δ were synthesized (using 6N Cd, Zn and
Te), melted and rapidly cooled in evacuated (up to
10–2 Pa) uncoated silica ampoules with diameter of 35 to
© 2005, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
110
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2005. V. 8, N 1. P. 110-113.
Fig. 1. Sketch of the growth ampoule and the temperature
profile in the Cd1–xZnxTe crystal growth zone by the Lo et al.
[10] method: 1 – furnace, 2 – charge, 3 – growing crystal.
Fig. 2. A modified in the present work ampoule and
temperature profile in the furnace for Cd1–xZnxTe vapor
growth: 1 – furnace, 2 – initial charge, 3 – capillary, 4 – silica
window, 5 – growing crystal.
40 mm. The compact boule was placed in the growth
ampoule which was evacuated with or without argon.
The crystal growth experiments were performed in a
two-zone furnace at 1053…1223 K. The temperature of
the excess component condensation zone varied between
600 to 1000 К. Computerized temperature control of the
initial charge, crystal growth and excess component
condensation zones was provided using Pt/PtRh
thermocouples with an accuracy ± 0.1 К. The nucleation
process control was carried out using a special optical
equipment up to complete fill of the container bottom in
the course of nucleation on the bottom or during whole
mass transfer process in the growing on the charge case.
Two types of the growing equipment were used
during the experiments. The growth ampoule and
temperature profile in the process of CdZnTe crystal
growth by the original method [10] are illustrated by
Fig. 1. The growth ampoule modified in this work is
schematically depicted in Fig. 2.
Fig. 3. Single crystals of Cd1–xZnxTe grown by the method
[10]: а – х = 0.13, b and с – 0.04. Initial charges were reached
by the metal component (a, b) and Te (c).
The obtained crystal structure was controlled by
metallographic and X-ray diffraction analysis methods.
Besides, the selective chemical etching was carried out
to determine the structure defect content and nature on
the (111) and (110) surfaces of the prepared from the
crystals wafers. The latter were polished in the Inoue
etchant [13] followed by etching in CrO3: HF: H2O [14]
or EAg-2 [13] solutions, accordingly. The structure
morphology caused by the Cd or Te excess defects and
the content of the latter were observed in an IR
transmission microscope at λ = 1 μm. The inclusions
nature was determined being based on elemental
analysis data obtained using an electron beam
microscope (JEOL).
The plates of 5×5×2 mm were cut from the ingot for
detectors production and then mechanically polished in
the fast polishing Inoue etchant [13] followed by the
etching in 0.5 % solution of Br2 in CH3OH to remove
damaged layers.
The type of conduction, concentration and mobility
of carriers in the obtained crystals were determined by
Hall measurements. Ohmic contacts to the samples and
diodes were produced by chemical deposition of Au
from HAuCl4 solution and tested by current-voltage
characteristics in the dark. Spectra of the planar
detectors were taken using irradiation of Ag110 and Cs137
sources.
3. Results and discussion
Though the method of Lo et al. [10] have been rather
successfully used in our experiments for vapor growing
the A4B6 crystals, perfect Cd0.96Zn0.04Te or Cd0.87Zn0.13Te
crystals were not obtained, probably, because of a more
narrow homogeneity region in A2B6 compounds [15, 16]
comparatively to A4B6 ones. The crystals which were
grown from the enriched by a metallic component
charges, had acicular surface structure (Fig. 3a, b)
independently on x value. When the starting charges had
an excess of Te, the obtained crystals were multigrain
(Fig. 3c). Besides, the crystals have a high content level
of the excess components. Thus, taking into account
rather small CdTe [15] and CdZnTe [16] homogeneity
region it must be concluded that it is necessary to fine
control over the component deviation from
stoichiometry during the growth process.
© 2005, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
111
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2005. V. 8, N 1. P. 110-113.
Fig. 4. Untransparent in IR-range inclusions in Cd0.96Zn0.04Te
crystals, grown from the charge, enriched by Cd (a) and Te (b).
The stacking fault in Cd0.96Zn0.04Te crystal, provoked by the
SiO2 flakes involved by the crystal (c).
© 2005, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
Fig. 5. a – An earlier stage of the Cd0.96Zn0.04Te crystal
growing process by the modified method [10]; b – the ampoule
with the single crystal (left) and the residual initial charge
(right).
Fig. 6. a – Cs-137 spectra of the Cd0.96Zn0.04Te crystal detector;
Ag110m spectra of the Cd0.87Zn0.13Te detector (b) and a standard
NaI (Tl) detector (c).
Microstructure investigations show a difference of
the second phase inclusion shape due to nature of the
abundant component in the initial charges. The excess of
the metallic component in the initial charge has resulted
in appearance of roundish or oval inclusions opaque in
IR-range (Fig. 4a). Based on the tellurium-enriched
initial charge, the grown crystals contain 3- or 6-edged
precipitates that observed as dark figures in IR
transmission microscope (Fig. 4b). The electron beam
investigations gave a possibility to obtain SiO2 in-
112
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2005. V. 8, N 1. P. 110-113.
clusions as the excess component or vacancies conden-
sation centers. Absorbed by the crystallization front the
flakes of SiO2, generated from the ampoule walls, create
stresses in the growing crystal due to a mismatch
between the lattice parameters of the crystal and SiO2.
Relaxation of strains in the crystal occurs due to migra-
tion of cadmium vacancies into the deformed range of
the crystal and their cooperation followed by creation of
tetrahedral stacking faults (Fig. 4c). Depending on the
crystal cooling conditions, such defects can serve as sites
for the excess component precipitations (Fig. 4b).
On the basis of the obtained data, it was concluded
that a crystallization front convex shape had a most
determinant influence on the crystal quality.
Minimization of a plastic deformation effect that caused
sub-grains and small-angle grain boundaries occurrence
can be provided by heat removal from the crystallization
front by radiation, not by the crystal thermal
conductivity. For this purpose, the proposed in this paper
modified ampoule construction had a beneficial effect.
As a result, we have obtained the single crystals of about
25 cm–3 dimensions, constrained by natural faces
corresponding to the (110), (100), and (111) planes
(Fig. 4). Measuring the rocking curves half-height width
for reflection planes (CuKα X-radiation) with the Miller
indices (111), (220), (311), (422), and (331) gave 25.0",
17.5", 13.6", 20.8", and 13.6" values, respectively. X-ray
patterns obtained with CuKα radiation do not reveal any
bulk defects or mechanical strains.
According to the microstructural study data, the
dislocation density can be minimized up to ~ 103 cm–2.
As a rule, room temperature resistivity of such crystals
increases symbaticly with Zn content increase. Both n
and p types of materials can be obtained by the deviation
from stoichiometry changing from n = 3·1014 cm–3 up to
p = 1.7⋅1015 cm–3, with carrier mobilities of 300 to
900 cm2/V·s and 50 to 70 cm2/V·s accordingly at 300 K.
The grown crystal shape and size were defined both
by the temperature gradient between growing and
condensation zone and the deviation from the
stoichiometry (vapor supersaturation). The single
crystals growing rate reached as high as 2 сm3/day.
Separate phases of the growth process are demonstrated
in Fig. 5. It must be noted that thought (111) plane
preferential growth was obtained in earlier stages, later
(100) plane becomes dominating. The best single
crystals were characterized by a low density of
dislocations (about 103 cm–2 in Cd0.87Zn0.13Te), minority
quantity of the SiO2 + Te-based inclusions that are the
usual defects grown by the Lo method [10], low X-ray
rocking curve width (13…25″).
Using Cd0.96Zn0.04Te1±δ + 0.2 Ga2Te3 alloy as an
initial source, there were obtained rather perfect single
crystals with 2⋅106 Ohm⋅cm resistivity at 300 K.
The obtained high-resistive solid solution crystals
were successfully tested as room temperature X-ray and
gamma-ray detectors. Fig. 6a shows a good resolution in
Cs137 β-ray spectra by Cd0.96Zn0.04Te sample at the field
strength U = 2000 V/cm. The high sensitivity to gamma-
ray radiation of Ag110m source have been demonstrated
for the Cd0.87Zn0.13Te-based detector (Fig. 6b).
Comparison of its spectra with those obtained by the
standard NaI (Tl) detector measured under identical
conditions (Fig. 6c) confirms this conclusion.
4. Summary
High-quality structure, high-resistive Cd1–xZnxTe
(x ≤ 0.13) single crystals of 30 to 35 mm in diameter
were grown from the vapor by contactless method using
the polycrystalline ternary compound as the source
material. It was obtained that, for preparation of high-
resistive perfect crystals at high growth rate, there is a
need of heat removal from the crystallization front by
radiation, not by the crystal thermal conductivity. The
obtained crystals were successfully tested for creating
the room temperature X-ray and gamma-ray detectors.
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© 2005, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
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