Online version is available on http://research.guilan.ac.ir/csm
CSM
Chemistry of Solid Materials
Vol. 2 No. 1 2014
[Research]
Preparation and growth of SnS thin film deposited by spray pyrolysis
technique
T. Akbari
1
, S.M. Rozati
2*
1
MSc Student, Department of Physics, Faculty of Sciences, University of Guilan, P. O.
Box: 41335-1914, Iran
2
Professor, Department of Physics, Faculty of Sciences, University of Guilan, P. O.
Box: 41335-1914, Iran
* Corresponding author’s E-mail: smrozati@guilan.ac.ir
Article history:
(Received: 29 Oct 2014, Revised: 28 Feb 2015, Accepted: 7 Mar 2015)
ABSTRACT
In this paper thin films of tin sulfide (SnS) were deposited on the glass substrates using spray
pyrolysis method with the substrate temperatures in the range of 400–600℃, keeping the other
deposition parameters constant. In this work the characteristic of SnS thin films investigated.
The XRD pattern and optical transmittance of thin films also are discussed. With the change in
concentration of thiourea, the physical properties of the thin films are also investigated.
Keywords: Tin sulfide, Spray pyrolysis, SnS thin film, Substrate temperature, Concentration.
1. INTRODUCTION
In recent years¸ much attention has
been focused on tin sulfide (SnS)
because of its potential use in the
fabrication of various applications such
as holographic recording systems¸ solar
collectors and solar photovoltaic cells.
SnS belongs to the IV-VI group of
layered semiconductors and crystallizes
in orthorhombic structure wherein the
Sn and S atoms are tightly bonded by
van der walls forces [1]. SnS has an
absorption coefficient of >10
with an optical band gap of 1.3 eV to
the optimum value of 1.5 eV¸ suitable
for solar cell applications [1¸2]. In
addition¸ the constituent elements of
this material are non-toxic and
abundant in nature. Thin films have
been deposited using a variety of
techniques such as chemical
deposition¸ electrochemical deposition,
electro deposition¸ chemical vapor
deposition and vacuum evaporation [1].
In this paper, SnS thin films have been
deposited using spray pyrolysis. This
technique is very suitable for large-
scale production of thin films and the
film thickness is easily controlled by
the quantity of the sprayed solution [3].
2. EXPERIMENTAL
Materials and method
Thin films of SnS were prepared by
spray pyrolysis using equimolar (0.1
M) solutions of tin chlorides ,
SnCl .2H O and thiourea (CS(NH2)2)
(Merck) onto glass substrates. The
substrates were cleaned by HCl acid,
acetone and ethanol. A mixture of 2-
propanol alcohol and deionized water
in the ratio 3:1 was used to prepare the
starting solution [3]. The substrate
temperature was kept in the range of
400-600 ℃ and the air pressure was T. Akbari, S.M. Rozati
/CSM Vol.2 No.1, 2014 pp.33-39
34
maintained at 2 . Compressed
purified air was used as a carrier gas.
The source to substrate distance was
about 32 cm. The structural properties
of the films were studied by X-ray
diffractometer.
The optical measurements were carried
out by using UV-Visible spectro-
photometer. The surface morphology of
deposited films is investigated by SEM
analysis. Then, by changing the
concentration of thiourea (Ms=0.2 and
Ms=0.4), the thin film properties were
studied (for this part, the optimum
temperature, 500℃ was used).
3. RESULTS AND DISCUSSION
According to the XRD pattern (Figure
1), at lower substrate temperature,
structure of the film is amorphous. As
the temperature increases gradually,
energy for crystal plates growth would
be provided. At 450 ℃ substrate
temperature, SnS phase would be
revealed, that is in good agreement
with the values of standard card
[JCPDS no.01-083-1758]. With further
increase in substrate temperature
(500 ℃), growth of SnS films
improved. By increasing the
temperature, possibly presence of
oxygen in the reaction and evaporation
of sulfide enhances [2]. This could be
the reason for the formation of binary
phases other than SnS (T=550℃ and
600℃). Thus we have chosen
T=500℃ as the optimum substrate
temperature.
Fig. 1. XRD pattern of the prepared thin films of tin sulphide by increasing the substrate
temperature.
T. Akbari, S. M. Rozati
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35
Table (1) presents the change in sheet
resistance, transparency and crystallite
size of tin sulfide thin films with
increasing substrate temperature.
Average crystallite size was estimated
by the Eq (1).
D = Kλ/βcosθ (1)
where K= 0.89 is the shape factor¸ λ is
the X-ray wavelength of Cu Kα
radiation (1.54 ˚A), is the Bragg
angle and is the experimental Full-
Width at Half Maximum (FWHM) of
the respective diffraction peak [4].
Table. 1. Changes of some properties in thin films of tin sulfide
Temperature
(℃)
Transparence
(%)
R
Ω/cm2
D(nm)
400 69 30 MΩ _
450 72 1 MΩ 14.2
500 73 7 KΩ 23.8
550 66 37 KΩ 27.9
600 71 5 MΩ 46.1
Fig. 2: Transmittance spectra of tin sulfide thin films
T. Akbari, S.M. Rozati
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36
As shown in the table, the average
crystallites size of the films increases
by increasing the substrate temperature.
At lower substrate temperature, high
electrical resistance was caused due to
the small grain size and hence
crystalline structure of the film has not
been formed properly. As the
temperature increases to 500℃, the
sheet resistance has a decreasing trend
while at 550℃, it increases. By a
proper bond forming, the film
resistance could be improved.
Beside, with the creation of additional
binary phases, the sheet resistance of
the films would increase. It is also
expected to observe the growth of
grains with an increase in temperature.
On the other hand the mobility of the
prepared films would have a low value
at higher substrate temperature [2].
The transparency of the thin films is
shown in Figure 2. It is obvious that the
transparency is about 69% at 400℃ and
it changes to 73% at 500℃. However,
it reduced to 66% at 550 ℃ and 71% at
600 ℃ substrate temperature. At higher
temperature, the thermal energy
provides bond formation thus it leads to
have an increase in transparency.
Fig. 3: The SnS Thin films picture in T=450℃(a), T=500℃ (b), T=550℃(C)
T. Akbari, S. M. Rozati
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37
Figure 3 demonstrate the SEM
morphology of SnS thin films
deposited at various substrate
temperatures. As shown in the figure,
the process of the grain growth, film
structure and the uniformity of the
films are observed which could be due
to the splitting of tin-sulfur bond [2, 3].
In Figure 4, the XRD pattern for thin
films with increasing in concentration
of thiourea is shown. According to it,
with increasing the thiourea concen-
tration, the spectrum showed a strong
peak oriented along (111) that is in
agreement with the results of other
workers [5-7]. This can indicate that by
increasing the amounts of sulfide, the
reaction conditions improve. Thus, we
can expect that transparency increases
because the condition of formation of
the films is met as in Figure 5.
Fig. 4: The XRD pattern of the prepared thin films of tin sulphide by increasing thiourea
concentration
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38
Fig. 5: Transmittance spectra of tin sulfide thin films
4. CONCLUSION
Tin sulfide polycrystalline films were
deposited on glass substrates by spray
pyrolysis technique. Substrate
temperature and the concentration of
thiourea can influences over the films
structure and the optical properties. At
lower substrate temperature, thin films
are exhibited an amorphous structure
while at higher temperature, the
additional different phases such as SnS2
and Sn2S3 are observed. As the
substrate temperature increases to
500℃, the sheet resistance has a
decreasing trend (7 KΩ/cm2
) while at
550℃, it increases to 5 MΩ /cm2
. .By
changing the thiourea concentration,
the films physical properties is
changed. The prepared films exhibited
SnS phase with strong peak at 31.9°
corresponding to (111) orientation.
Thus, the transparency increases due to
the condition of formation of the films.
Acknowledgements
The authors gratefully acknowledge the
research department of University of
Guilan.
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