Luminescent and transport properties of metastable quaternary compounds in the Cd, MIII ∥ S, Te (MIII = In, Ga) systems

Article abstract of DOI:10.1007/s10789-005-0059-3

Metastable quaternary compounds in the reciprocal systems Cd, M ∥ S, Te (M = In, Ga) are prepared by liquid quenching, and their luminescent and transport properties are studied for the first time. Cd₃In ₂S₂Te₄,

Full text of DOI:10.1007/s10789-005-0059-3

Inorganic Materials, Vol. 40, No. 12, 2004, pp. 1252–1254. Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1427–1430.
Original Russian Text Copyright © 2004 by Odin, Chukichev, Rubina.
Luminescent and Transport Properties
III
of Metastable Quaternary Compounds in the Cd, M || S, Te
III
(
M = In, Ga) Systems
I. N. Odin, M. V. Chukichev, and M. E. Rubina
Moscow State University, Moscow, 119899 Russia
e-mail: odin@inorg.chem.msu.ru
Received November 20, 2003; in final form, July 9, 2004
Abstract—Metastable quaternary compounds in the reciprocal systems Cd, M || S, Te (M = In, Ga) are prepared
by liquid quenching, and their luminescent and transport properties are studied for the first time. Cd In S Te ,
3
2
2
4
Cd Ga S Te , Cd Ga S Te , and CdGa S Te are photosensitive and exhibit efficient near-IR or red
3
2
2
4
2
2
2
3
2
2
2
(
CdGa S Te ) luminescence. The properties of the compounds Cd M S Te (M = In, Ga) are also described.
2 2 2 2 6 2 9
All of the synthesized compounds are semiconductors. Their band gaps are evaluated from luminescence data.
The peak positions in their luminescence spectra are found to be composition-independent within the homoge-
neity ranges of Cd M S Te –Cd M S Te (M = In, Ga).
3
2
2
4
5
2
2
6
INTRODUCTION
into a saturated aqueous NaCl solution maintained at
2
73 K. The cooling rate was about 190–200 K/s.
The Cd, Ga || S, Te system was studied in [1]. At
Characterization techniques. Phase composition
of the samples was determined by x-ray diffraction
7
55 K, the stable equilibria in this system involve solid
solutions based on constituent components and ternary
(
XRD) using an FR-552 Guinier focusing camera. Den-
compounds. The quaternary compounds Cd Ga S Te ,
3
2
2
4
sity was determined by the Archimedes method using
extrapure-grade bromoform additionally purified by
double distillation as the buoyancy fluid. Microstruc-
tures were examined under an MII-4 optical micro-
scope. Electron probe x-ray microanalysis (EPXMA)
was performed with a Cameca instrument.
Cd Ga S Te , CdGa S Te , and Cd Ga S Te were
2
2
2
3
2
2
2
2
6
2
9
obtained in a metastable state. The exchange reaction
Cd S + In Te Cd Te + In S has not yet been
3
3
2
3
3
3
2 3
studied. Our results indicated the existence of the qua-
ternary compounds Cd In S Te and Cd In S Te . Mul-
3
2
2
4
2
6
2
9
ticomponent cadmium chalcogenide compounds are of
practical interest as potential photosensitive materials.
The carrier concentration and mobility were
inferred from four-probe electrical conductivity and
Hall effect measurements. CL and photoconductivity
In this work, we report the cathodoluminescence
(
CL) spectra and transport properties of quaternary
(PC) spectra were recorded as described elsewhere [2].
compounds in the systems in question.
RESULTS AND DISCUSSION
EXPERIMENTAL
Synthesis and XRD characterization of quater-
Starting materials. In our preparations, we used
high-purity CdS single crystals grown by the Markov–
Davydov method. The impurity composition of the
crystals was specified in a previous study [2]. High-
purity CdTe single crystals were prepared by vapor
phase growth. Mixed chalcogenides were synthesized
nary metastable compounds. New metastable chalco-
genides were prepared by quenching superheated melts
from 1320–1330 K. At high temperatures, the intermix-
ing of particles in the melt leads to the formation of
both M–S and M–Te bonds. In light of this, quenching
(
cooling at a rate of about 200 K/s) was expected to
from CdS, Ga S , Ga Te , In Te , In S , and CdTe. The
2
3
2
3
2
3
2 3
ensure the formation of metastable quaternary com-
indium and gallium chalcogenides were prepared from pounds.
Ekstra V-4 tellurium, 3N indium, 3N gallium, and
OSCh 16-5 sulfur (sulfur was additionally purified by
vacuum distillation).
In this way, we obtained a number of metastable
compounds in the Cd, M || S, Te (M = In, Ga) systems.
It seems likely that their formation proceeded through
Synthesis of mixed chalcogenides. Synthesis was diffusionless crystallization. This assumption is sup-
carried out in graphitized silica tubes. Metastable qua- ported by the fact that the samples were single-phase,
ternary compounds were prepared by liquid quenching with no second-phase inclusions, as determined by
from 1320–1330 K. To this end, the tubes were dropped EPXMA and microstructural analysis. The process was
0
020-1685/04/4012-1252 © 2004 MAIK “Nauka/Interperiodica”

LUMINESCENT AND TRANSPORT PROPERTIES
1253
reproducible: in some cases, identical results were
obtained in up to ten experiments. The exchange reac-
tion Cd S + In Te Cd Te + In S yields no stable
9
47
3
3
2
3
3
3
2 3
quaternary compounds (the 755-K section of the phase
diagram in question will be reported in a forthcoming
paper).
1
The homogeneity ranges of the compounds
Cd M S Te include the compositions Cd M S Te
1
022
3
2
2
4
5
2
2
6
(
phase I for M = Ga and phase V for M = In). We
assume that the formula of these compounds is
Cd M S Te rather than Cd M S Te because the XRD
3
2
2
4
5
2
2
6
2
peaks from Cd M S Te are broader than those from
5
2
2
6
Cd M S Te . At CdTe contents above that of
3
2
2
4
Cd M S Te , the samples consist of phase I or V and a
5
2
2
6
CdTe-based solid solution. Compound I has an fcc
(
sphalerite) structure, and compoundV has a hexagonal
wurtzite) structure. No superlattice reflections were
(
3
detected in the XRD patterns of Cd M S Te and
3
2
2
4
708
Cd M S Te (M = In, Ga), which attests to random dis-
5
2
2
6
tributions of Cd, M, cation vacancies, S, and Te. Möss-
bauer studies of these compounds also revealed no
ordering (the results will be presented in a forthcoming
paper).
7
50
7
39
4
The lattice parameters of Cd In S Te are a =
Wavelength, nm
3
2
2
4
0
.4344(4) nm and c = 0.7103(6) nm. The unit-cell vol-
7
8-K CL spectra of (1) Cd Ga S Te , (2) Cd In S Te ,
3 2 2 4 3 2 2 4
ume of the wurtzite phase is V = 0.1161 nm . The total
w
3
(3) Cd Ga S Te , and (4) CdGa S Te .
2 2 2 3 2 2 2
hexagonal cell contains one Cd In S Te formula unit:
Vtotal = 3V = 0.3483 nm . All of the anion sites are
3
2
2
4
3
w
occupied by S and Te, whereas some of the cation sites
tions and Ga S Te. Cd In S Te decomposes into a
2
2
3
2
2
4
are vacant: (Cd In ꢀ)(S Te ). The measured density
3
2
2
4
mixture of CdIn S , CdIn Te , and CdTe. Cd Ga S Te
2 4 2 4 2 6 2 9
3
(
(
5.42 ± 0.01 g/cm ) is close to the x-ray density
decomposes into a mixture of Ga S Te, CdTe, and
2
2
3
5.44 g/cm ).
CdGa Te ; and Cd In S Te , into a mixture of CdIn S ,
2
4
2
6
2
9
2 4
Cd Ga S Te (phase I) has the sphalerite structure CdIn Te , and CdIn Te .
5
2
2
6
8
13
2
4
with a = 0.6415(5) nm and a unit-cell volume V =
s
At room temperature, these quaternary compounds
may persist for a long time (at least a year).
3
0
.2640 nm (half of a Cd Ga S Te formula unit per
5
2
2
6
cell). All of the anion sites are occupied by S and Te
atoms, whereas some of the cation sites are vacant:
7
3
8-K CL spectra. The CL spectrum of
Cd Ga S Te shows only one line, at 947 nm (figure,
(
0
Cd Gaꢀ )STe . The measured density (4.79 ±
2
2
4
2
.5
0.5
3
3
3
spectrum 1), due to edge emission. The band gap E
g
.01 g/cm ) is close to the x-ray density (4.81 g/cm ).
evaluated from its position is 1.31 eV. The spectrum of
Cd In S Te also shows a single line, at 1022 nm (spec-
Cd In S Te (phase VI) has an fcc (sphalerite) struc-
2
6
2
9
3
2
2
4
ture with a = 0.6415(5) nm.
Cd Ga S Te (phase II) has a rhombohedrally dis-
trum 2), which corresponds to E = 1.21 eV. A notewor-
g
2
2
2
3
thy feature of single-phase samples of phase V is that,
torted sphalerite structure with a = 0.6395(5) nm and
α = 98.35(7)°. The XRD patterns of phases II and VI
showed no superlattice reflections.
even though Cd In S Te and Cd In S Te differ drasti-
3
2
2
4
5
2
2
6
cally in composition (Te : S = 2 : 1 and 3 : 1, respec-
tively), the peak positions in their CL spectra differ very
Compound IV (Cd Ga S Te ) has an fcc subcell little (Table 1), as do those in the spectra of
2
6
2
9
with a = 0.5969(5) nm. The presence of weak superlat- Cd Ga S Te and Cd Ga S Te (phase I). This is proba-
3
2
2
4
5
2
2
6
tice reflections in its XRD pattern attests to a more bly due to the random distributions of Cd, M, cation
complex crystal structure.
vacancies, S, and Te in the structures of phases I and V.
CdGa S Te (phase III) crystallizes in the tetragonal
system with a = 0.7058(5) nm and c = 1.0164(7) nm.
2
2
2
The CL spectrum of Cd Ga S Te shows a single
line, at 928 nm, corresponding to edge emission (figure,
2
2
2
3
All these compounds are metastable and, during spectrum 3). CdGa S Te exhibits edge emission in the
2
2
2
annealing at 755 K, decompose into mixtures of equi- red spectral region (spectrum 4). An important point is
librium phases. Cd Ga S Te , Cd Ga S Te , and that the quaternary compounds with a cubic structure
3
2
2
4
2
2
2
3
CdGa S Te decompose to form CdTe-based solid solu- (Cd Ga S Te ) or a slightly distorted cubic structure
2
2
2
3
2
2
4
INORGANIC MATERIALS Vol. 40 No. 12 2004

1
254
ODIN et al.
Table 1. Peak position of edge emission in the CL spectrum ductivity, hole concentration, and hole mobility) are
and band gap of metastable quaternary compounds
Wavelength, nm Eg, eV
8 K 298 K 78 K 298 K
summarized in Table 2. It is of interest to note that, in
different samples within the homogeneity ranges of
Cd M S Te –Cd M S Te (M = In, Ga), the hole con-
centration and mobility are constant to within the
present measurement accuracy (Table 2).
3
2
2
4
5
2
2
6
Phase Composition
7
I
Cd Ga S Te
947
947
928
708
961
962
963
1.31
1.31
1.33
1.75
1.29
1.21
1.21
1.19
1.29
1.29
1.30
1.73
1.27
1.23
1.23
1.18
3
2
2
4
6
3
Cd In S Te , Cd Ga S Te , Cd Ga S Te , and
3
2
2
4
3
2
2
4
2
2
2
3
I
Cd Ga S Te
CdGa S Te are photosensitive, with a ratio of dark to
5
2
2
2 2 2
3
light (10 lx) resistance of 430, 720, 850, and 980,
respectively. The compounds Cd In S Te (M = In, Ga)
II
Cd Ga S Te
954
2
2 2
2
6
2
9
III
IV
V
V
VI
CdGa S Te
2
715
2
2
have an insignificant photoresponse. The 298-K PC
spectra of Cd Ga S Te , Cd In S Te , and
Cd Ga S Te show each a single peak, at 960, 1010,
Cd Ga S Te
972
2
6
2
9
3
2
2
4
3
2
2
4
Cd In S Te
1022
1022
1036
1006
1007
1042
2
2
2
3
3
2
2
4
and 955 nm, respectively. The spectrum of CdGa S Te
2
2
2
Cd In S Te
5
2
2
6
shows a peak at 715 nm with a shoulder at 750 nm.
Cd In S Te
2
6 2
9
CONCLUSIONS
Table 2. Transport properties of p-type metastable quater-
Metastable quaternary compounds in the reciprocal
systems Cd, M || S, Te (M = In, Ga) were prepared by
liquid quenching.
nary compounds
N × 10–16,
2
Phase Composition
–3
µ, cm /s
σ, S/cm
cm
XRD data for Cd In S Te , Cd Ga S Te , and
3
2
2
4
3
2
2
4
Cd Ga S Te attests to random distributions of Cd, M,
2
2
2
3
I
Cd Ga S Te
7.2
7.2
6.5
1.1
8.4
9.6
9.6
11.3
90
88
0.013
0.019
0.021
0.001
0.045
0.032
0.038
0.059
3
2
2
4
6
3
cation vacancies, S, and Te in their structures. These
I
Cd Ga S Te
5 2 2
compounds are photosensitive and exhibit efficient
near-IR luminescence. CdGa S Te exhibits red lumi-
II
Cd Ga S Te
99
2
2
2
2
2 2
nescence.
III
IV
V
V
VI
CdGa S Te
2
81
2
2
The luminescent properties of the compounds stud-
ied are composition-independent within the homogene-
ity ranges of Cd M S Te –Cd M S Te (M = In, Ga).
Cd Ga S Te
105
109
105
112
2
6
2
9
Cd In S Te
4
3
2
2
3
2
2
4
5
2
2
6
Cd In S Te
These compounds, disordered in both the cation and
anion sublattices, have interesting structural and physi-
cal properties.
5
2
2
6
9
Cd In S Te
2
6 2
(
Cd Ga S Te ), as well as the compound with the
2 2 2 3
ACKNOWLEDGMENTS
wurtzite structure (Cd In S Te ), exhibit efficient IR
luminescence at 78 K.
3
2
2
4
This work was supported by the Russian Foundation
for Basic Research, grant no. 02-03-32916.
2
98-K CL spectra. The room-temperature CL
spectra of Cd Ga S Te , Cd Ga S Te , and
3
2
2
4
2
2
2
3
REFERENCES
Cd In S Te (and those for compositions lying in their
3
2
2
4
1
. Odin, I.N. and Rubina, M.E., System Cd S + Ga Te =
3 3 2 3
Cd Te + Ga S , Zh. Neorg. Khim., 2003, vol. 48, no. 7,
homogeneity ranges) also show a single line (Table 1),
which is slightly shifted as compared to the 78-K spec-
tra. The luminescence intensity at 298 K is lower than
that at 78 K.
3
3
2 3
pp. 1206–1208.
2. Odin, I.N., Chukichev, M.V., and Rubina, M.E., Lumi-
nescent Properties of CdS Crystals Doped with Gallium
and Tellurium in Cadmium Vapor, Neorg. Mater., 2003,
vol. 39, no. 7, pp. 793–795 [Inorg. Mater. (Engl. Transl.),
vol. 39. no. 7, pp. 669–671].
Transport properties and PC spectra. All of the
synthesized quaternary compounds are p-type semi-
conductors. Their transport properties (electrical con-
INORGANIC MATERIALS Vol. 40 No. 12 2004