1070-4272/02/7505-0715$27.00C2002 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 75, No. 5, 2002, pp. 715!719. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 5,
2002, pp. 734!738.
Original Russian Text Copyright C 2002 by Belyaev, Rubets, Kalinkin, Nuzhdin.
AND INDUSTRIAL INORGANIC CHEMISTRY
Analysis of Electrical Properties of Thin Film Samples
in the Course of Phase Transformations of Cadmium Sulfide
and Telluride Solid Solutions
A. P. Belyaev, V. P. Rubets, I. P. Kalinkin, and M. Yu. Nuzhdin
St. Petersburg State Technological Institute, St. Petersburg, Russia
Received June 3, 2000; in final form, September 2001
Abstract-Phase transformations in layers of cadmium sulfide and telluride solid solutions, synthesized under
nonequilibrium conditions, are studied. Thermally activated decomposition of a single-phase CdS
1 3 x
tion containing an a
= 0.430.6) into two phases, a
= 0.13 0.2) and a
= 0.783 0.99), is
chosen as a model process. Electron diffraction patterns and temperature dependences of photoconductivity
and conductivity, measured both in the course of phase transformations and after them, are presented. The
results of electrical studies are compared with structural data.
Solid solutions based on compounds of Group II
and VI elements (II3VI compounds) show promise
as materials for microelectronics owing to their widely
varying properties. These materials are used in devel-
oping photoelectric converters, detectors of ionizing
radiation, and sensors of gaseous chemical com-
pounds. Among the factors hindering their wider use
are phase transformations occurring in solid solutions
in the course of time. In this connection, an attempt is
made here to trace the course of transformations in
a typical system, CdS3CdTe . There has been vir-
tually no reports on experimental studies of this kind.
This is presumably due to the limited sensitivity and
complexity of continuous monitoring by means of
structural analytical methods widely used to study the
phase composition of substance.
It is known that the electrical properties of a sub-
stance are the most sensitive to its structural state. The
prospects for use of electrical properties to analyze
materials were mentioned already by Kurnakov .
However, studies concerned with application of elec-
trical measurements to analysis of phase transforma-
tions are still virtually lacking. Here we attempt
to use current transport measurements as a tool in
analysis of thermally activated phase transformations
Samples obtained in a vacuum (residual pressure
Pa) by the thermal shield method under strongly
nonequilibrium conditions were studied [3, 4].
A mechanical mixture of CdS and CdTe powders
taken in 40 : 60 (at. %) ratio was subjected to thermal
evaporation. Small sheets of mica (muscovite) served
as substrates for condensation. The nonequilibrium
conditions were chosen because of the necessity to
obtain samples prone to phase transformations.
The thus prepared samples were CdS
with polycrystalline structure, composed of 0.13
0.2-mm crystals of the cubic modification and definite
chemical composition. The composition of the solid
solution was constant within a sample. Samples with
0.4 < x < 0.6 were studied. The uniformity of the
solid solution throughout the sample volume and its
specific composition were found by electron diffrac-
tion. All structural and morphological studies were
carried out with EMR-100 electron diffractometer and
PEM-100 electron microscope. The electron diffrac-
tion patterns were identified using the ASTM file.
The sample thickness was varied in the range
0.3030.50 mm. Within a sample, the layer thickness
was constant and invariable in the course of experi-
ments. The thickness was measured on an MII-4 mi-
crointerferometer with accuracy of +0.03 mm.
All the techniques employed to measure electrical
and photoelectric characteristics  were chosen with
account of the fact that solid solution layers are semi-
conducting film materials . Electrical measure-
ments were carried out in a vacuum (residual pressure
Pa), in which samples were kept for several days.