Preparation and growth of SnS thin film deposited by spray pyrolysis technique

 
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
 
/CSM Vol.2 No.1, 2014 pp.33-39
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
 
/CSM Vol.2 No.1, 2014 pp.33-39
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
 
/CSM Vol.2 No.1, 2014 pp.33-39
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
 
 
 
 
 
 
 
 
 
 
 
 
 
 T. Akbari, S.M. Rozati
 
/CSM Vol.2 No.1, 2014 pp.33-39
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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