International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
ISSN 2319 - 4847
Special Issue for National Conference On Recent Advances in Technology and Management for
Integrated Growth 2013 (RATMIG 2013)
Study of Spray Pyrolytically Deposited CuInSTe
Thin Films
Yashwantrao.D.Tembhurkar
Department of Physics, S.K.Porwal Collage, Kamptee
Email-id:-y_dt@rediffmail.com
Abstract
Spray pyrolysis is a very cheap and inexpensive method of depositing thin films of large area. We have deposited thin films CuInSTe on
glass substrates at 3250C by this method, using aqueous solutions of Copper chloride, Indium tri-chloride, Thiourea and Tellurium chloride
and studied their structural and electrical properties. CuInSTe is a promising chalcopyrite semiconducting material used for solar cell
fabrication. From the X-ray diffraction pattern the chalcopyrite structure of these films was confirmed with a =5.516 Å and c = 11.103 Å the
film were polycrystalline. Resistivity of the films was measured for temperature 77 K to 473 K. Variable Hopping Conduction Mechanisms
arises at very low temperature due to small grain size. The Hall Mobility and Carrier concentration at room temperature were calculated
using Van der Pauw-Hall Method.
Keywords: - CuInSTe thin Films, chalcopyrite semiconductor, and Electrical properties .
1. Introduction
Among the I-III-VI group material, ternary chalcopyrite compound is the leading semiconductor materials due to low cost and
abundance of the constituent element. Further, these compounds shall be useful in photovoltaic or optoelectronic devices because
(a) are direct band gap semiconductors with high absorption coefficient (b) can be easily obtained in the thin film form; either n or
p- type (c) have energy band gap (1-2eV) in the optical range for solar energy conversion (d) have lattice constant which matches
that of CdS, widely used in solar cell technology. There are several method to prepare thin film such as chemical vapour
deposition [1], [2], atomic layer epitaxy [3], white sol gel [4], spin [5], dip coating [6] and spray pyrolysis method [7] employ
precursor solutions.
We have chosen the economical and convenient method of chemical spray pyrolysis for deposition of thin films. Spray
pyrolysis does not required high-quality substrates or chemicals. The method has been employed for the deposition of dense films,
porous films and for powder production. Spray pyrolysis has been used for several decades in the glass industry and in solar cell
production. Typical Spray pyrolysis equipment consists of an atomizer, precursor solution, substrate heater and temperature
controller.
We have deposited CuInSTe thin films by this method and study their structural, electrical properties, Hall mobility and carrier
concentration. The electrical conductivity for temperature ranging from 77 K to 473 K calculated by using conventional Fourprobe method. The conductivity type of the films was determined by hot-probe method. Hall mobility and carrier concentration at
room temperature were determined by using Van der Pauw-Hall method. Thickness of the films was measured by using a
Michelson interferometer. Structural parameters were calculated by Phillips x-ray diffraction using wavelength 1.542 Å with Cu
Kα with radiation.
2. Experimental
details
An aqueous solutions of copper chloride, Indium tri-chloride, Thiourea and Tellurium chloride of 0.02 M of each were
prepared in double distilled water. The chemical used were of AR grade. Here, for preparing CuInSTe thin films, we have mixed
solution in the ratio 1:1:2.2:2.2 by volume. Excess Sulphur and Tellurium is necessary to obtain CuInSTe. The films deposited
have a Sulphur or tellurium deficiency if the ratio of solutions taken as 1:1:1:1. The excess selenium or tellurium is used to
remove this deficiency [8]. Biological glass slides were used as substrates. The temperature of the substrate, measured by a pre-
Organized By: GNI Nagpur, India
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
ISSN 2319 - 4847
Special Issue for National Conference On Recent Advances in Technology and Management for
Integrated Growth 2013 (RATMIG 2013)
calibrated copper costantan thermocouple was maintained at 3250C, which was the most suitable for the production of CuInSTe
thin films. The spraying rate of 3.5 ml/min was maintained. The distance between the sprayer nozzle and substrate was 30 cm.
The glass sprayer was mechanically moved to and fro during spraying to avoid the formation of droplets on the hot substrates and
to ensure instant evaporation.
3. Structural
properties
Fig.1 shows the x-ray diffraction pattern for as-deposited films of CuInSTe. CuKα -radiation with wavelength of 1.542 Å was
used and confirms the dominantly chalcopyrite structure of the films. Peak heights are slightly different with the data reported for
the bulk materials [9], [10]. A pronounced diffraction peak corresponding to the 112 plane indicates preferred orientation as the
direction of the 112 plane is least energy oriented for tetragonal systems. The other prominent peaks corresponding to the
204,031,116 are also present while reflections from the 011, 101, 325, and 424 planes remain weak. The structural parameters a
and c calculated from the XRD patterns of polycrystalline films are 5.516 Å and c = 11.103 Å respectively and are in good
agreement with Soliman [11] reported for thermal evaporation method. The values for our sprayed films therefore differ from the
standard value by 0.004 and 0.023 Å respectively. The value of tetragonal distortion (∆=2-c/a) was found to be negative and equal
to 0.0128, indicating built-in dilation c > 2a, which means compression [12]. Single crystal diffraction was not possible with the
present materials since the grain size of the films was too small. Due to the fact that the lattice constant value for ternary
compound family have a range of existence as high of 0.6 %.
Fig.1.X-ray diffraction pattern of as-deposited CuInSTe thin films
4. Electrical
Properties
The temperature dependence of the electrical conductivity of CuInSTe thin films was determined for two different ranges of
temperature. Range (a) was from 300 K to 473 K and range (b) was from 77 K (liquid nitrogen temperature) to 273 K. The
resistivity in range (a) was measured at atmospheric pressure and in range (b) at 10 -2 torr, for which a four-probe arrangement
together with sample film was enclosed in a specially prepared stainless steel container which was immersed in liquid nitrogen
bath. The conductivity of the films as determined by the hot probe method was of p-type.
Organized By: GNI Nagpur, India
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
ISSN 2319 - 4847
Special Issue for National Conference On Recent Advances in Technology and Management for
Integrated Growth 2013 (RATMIG 2013)
0.8
0.6
ln( σ)
0.4
0.2
1/T ×10 3
0
-0.2 2
4
6
8
10
12
-0.4
-0.6
-0.8
Fig.2 Arrhenius plot of conductivity of CuInSTe thin
Films
Fig.2 shows the Arrhenius plot of conductivity vs inverse temperature for the temperature ranges from 77 K to 473 K.
The plot suggests that there are three type of conductivity mechanisms that contribution to the conductivity. The conductivity of
the films increases with increasing temperature, indicating the semiconducting behavior of the films but the increase is slow in the
low temperature region upto 225 K. Above 225 K the conductivity increases linearly. The curves suggest that there are three types
of conduction mechanism that contribute to the conductivity. Activation energy calculated for these three regions are 80 meV, 54
meV and 5 meV for the temperature ranges 300 K-473 K, 160 K-250 K and 90 K- 125 K respectively. The Arrhenius plot can
yield the different levels which are responsible for different donar or acceptor mechanism. The change in the carrier mechanism is
indicated by the change in the slope of the curve [13]. As the conductivity of the film is p-type, acceptor-like levels are expected
to be present.
Tell et al [14] and migliorato et al [15] suggested that in Cu-III-VI ternary compound Cu and In vacancies act as acceptor
levels. As Cu participates very weakly in covalent bond formation, Cu vacancies are more probable than In vacancies. Activation
energy of 54 meV obtained in our investigation is in fairly good agreement with Soliman [11]. They have value reported 58.3
meV by in thermal evaporation method and therefore may be attributed to Cu vacancies. The straight line nature of the plot also
indicates the pressure of a grain boundary effect.
In the low temperature region that is 90 K- 125 K, the activation energy is 5 meV, which appears to be due variable range
hopping conduction mechanism. This can be verified in accordance with the relation [16],
σ α exp (-T0/T 1/4)
(1)
Organized By: GNI Nagpur, India
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
ISSN 2319 - 4847
Special Issue for National Conference On Recent Advances in Technology and Management for
Integrated Growth 2013 (RATMIG 2013)
2.1
2
ln(σT1/2)
1.9
1.8
1.7
1.6
0.29
0.31
T -1/4
0.33
Fig.3 Plot of ln(σT1/2) vs T-1/4 showing hopping
conduction
Fig.3 shows that the plot of ln (σT 1/2) vs 1/T-1/4 for this temperature range is linear, which indicates the presence of variable
range hopping conduction mechanism. The similar result for thermal evaporated CuInSeTe, CuInSeS and CuInSeTe thin films
have been reportd by soliman [11].
5. Hall
mobility and carrier concentration at room temperature
Hall coefficient at room temperature was determined by using the Van der Pauw-Hall technique [17]. The Hall mobility and
carrier concentration were calculated. The Hall mobility and carrier concentration at room temperature was found to be 1.95 cm2
V-1S-1 and 8.36×1017 cm-3 which is of the same order as that obtained by Soliman [11] for thermally evaporated method.
6. Conclusion
We conclude that p-type CuInSTe polycrystalline films can be deposited by spray pyrolysis. Thin film of CuInSTe have been
structurally investigated by X-ray diffraction technique. The structure is predominantly chalcopyrite with the tetragonal phase.
The films have preferred orientation along 112 directions. As the conductivity of the films is p-type, accepters like levels are
expected to be present. Variable range hopping conduction mechanism observed in low temperature region.
Acknowledgments
Author would like to express his thanks to the University Grants Commission, New Delhi for financial support in the form of
Major Research Project and Dr.S.S.Dhondge Principal, S.K.Porwal College Kamptee for a providing research facility in the
laboratory.
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Organized By: GNI Nagpur, India
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
ISSN 2319 - 4847
Special Issue for National Conference On Recent Advances in Technology and Management for
Integrated Growth 2013 (RATMIG 2013)
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