Some studies on successive ionic layer adsorption and reaction (SILAR) grown indium sulphide thin films

Article abstract of DOI:10.1016/j.materresbull.2005.02.013

Indium sulphide (In₂S₃) thin films were grown on amorphous glass substrate by the successive ionic layer adsorption and reaction (SILAR) method. X-ray diffraction, optical absorption, scanning electron microscopy (SEM) and Rutherford back scattering (RBS) were applied to study the structural, optical, surface morphological and compositional properties of the indium sulphide thin films. Utilization of triethanolamine and hydrazine hydrate complexed indium sulphate and sodium sulphide as precursors resulted in nanocrystalline In₂S₃ thin film. The optical band gap was found to be 2.7 eV. The film appeared to be smooth and homogeneous from SEM study.

Full text of DOI:10.1016/j.materresbull.2005.02.013

Materials Research Bulletin 40 (2005) 1018–1023
www.elsevier.com/locate/matresbu
Some studies on successive ionic layer adsorption and
reaction (SILAR) grown indium sulphide thin films
a
H.M. Pathan , C.D. Lokhande , S.S. Kulkarni ,
a,
a
*
b
b
D.P. Amalnerkar , T. Seth , Sung-Hwan Han
c
a
Thin Film Physics Laboratory, Department of Physics, Shivaji University, Kolhapur 416 004, India
Centre for Materials for Electronic Technology (C-MET), Off Pashan Road, Panchavati, Pune 411 008, India
b
c
Inorganic Nano-Materials, Department of Chemistry, Hanyang University, Sungdong-Ku,
Haengdang-dong 17, Seoul 133-791, Republic of Korea
Received 21 February 2004; received in revised form 30 December 2004; accepted 25 February 2005
Abstract
Indium sulphide (In S ) thin films were grown on amorphous glass substrate by the successive ionic layer
2
3
adsorption and reaction (SILAR) method. X-ray diffraction, optical absorption, scanning electron microscopy
SEM) and Rutherford back scattering (RBS) were applied to study the structural, optical, surface morphological
(
and compositional properties of the indium sulphide thin films. Utilization of triethanolamine and hydrazine
hydrate complexed indium sulphate and sodium sulphide as precursors resulted in nanocrystalline In S thin film.
2
3
The optical band gap was found to be 2.7 eV. The film appeared to be smooth and homogeneous from SEM study.
2005 Elsevier Ltd. All rights reserved.
#
Keywords: A. Chalcogenides; B. Thin films; C. X-ray diffraction; D. Optical properties
1
. Introduction
The application of indium sulphide thin films in solar cells as a window/buffer layer has been well
known [1,2]. The commonly used method to deposit indium sulphide thin film is chemical bath
deposition (CBD) [1–6] from aqueous solution. The indium sulphide films deposited by CBD are
*
Corresponding author. Tel.: +91 231 2690571; fax: +91 231 2691533.
E-mail addresses: l_chandrakant@yahoo.com (C.D. Lokhande), shhan@hanyang.ac.kr (S.-H. Han).
0025-5408/$ – see front matter # 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2005.02.013

H.M. Pathan et al. / Materials Research Bulletin 40 (2005) 1018–1023
1019
generally amorphous and depending on the substrate, the film is polycrystalline [2]. Similarly to CBD,
the growth process in the successive ionic layer adsorption and reaction (SILAR) method is carried out at
room temperature utilizing aqueous solutions. The basic difference between CBD and SILAR is growth
mode. In CBD, the precursors are present in same reaction vessel where as in SILAR, the substrate is
treated separately with each precursor. Recently, Mane and Lokhande [7] have reported the SILAR
deposition of In S thin films using indium chloride and sodium sulphide precursors having cubic crystal
2
3
structure and band gap equal to 2.3 eV.
In the present investigation, indium sulphide thin films were grown by SILAR using triethanolamine
(TEA) and hydrazine hydrate (HH) complexed indium sulphate and sodium sulphide precursors. The aim
of this paper is to study the structural, optical, surface morphological and compositional properties of
SILAR grown indium sulphide thin films using X-ray diffraction, optical absorption, scanning electron
microscopy (SEM) and Rutherford backscattering (RBS) techniques, respectively.
2
. Experimental
The growth of indium sulphide thin films was carried out by utilizing the successive ionic layer
adsorption and reaction (SILAR) method at room temperature. The aqueous precursor solution of
indium sulphate is complexed with TEA and HH (pH ꢀ 5). The source of sulphur ion was sodium
sulphide (pH ꢀ 12). One SILAR grown cycle consist of four steps: (1) adsorption of complexed
indium ions, (2) rinsing with distilled water to remove excess adsorbed or loosely bounded complexed
indium ions, (3) reaction with sulphide precursor solution to form stable indium sulphide and (4)
rinsing with purified water to remove excess or unreacted species or powdery indium sulphide. This
completes one deposition cycle of indium sulphide thin film. By repeating such cycles for finite
number of times indium sulphide thin films can be obtained. The optimized deposition conditions are
tabulated in Table 1.
The crystal structure was determined with a Philips PW-3710 X-ray diffractometer using Cu Ka
˚
radiation (l = 1.5406 A). The optical absorption was measured with UV-VIS-IR spectrophotometer
Hitachi-330 (Japan). The surface morphology of the film was characterized with a Philips XL-30
+
scanning electron microscope (SEM) and RBS data were obtained using 1.8 MeV He ions.
3
. Results and discussion
3
.1. Reaction mechanism
The formation of In S involves the following steps: the anionic precursor act as a source of sulphide
2
3
ions in alkaline medium as
Na S ! 2Na þ S2À
þ
(1)
(2)
2
3
In ions from complexed In(TEA + HH) are released as
+
3+
InðTEA þ HHÞ ! In3þ þ ðTEA þ HHÞ
3
þ

1
020
H.M. Pathan et al. / Materials Research Bulletin 40 (2005) 1018–1023
Table 1
Deposition conditions for SILAR grown indium sulphide thin films
Precursor
In
2
(SO
4
)
3
2
Na S
Concentration (M)
pH
0.08
0.05
ꢀ5
ꢀ12
25
Immersion time (s)
Number of immersions
Deposition temperature (K)
25
55
55
300
300
The following reaction takes place on the glass substrate
In þ 3S2À ! In2S3
3
þ
(3)
2
3
.2. Structural studies
According to X-ray diffraction pattern in Fig. 1, the indium sulphide (In S ) films grown on glass
2
3
substrate were nanocrystalline with rhombohedral crystal structure. The comparison of observed ‘d’ and
standard ‘d’ values [8] was made in Table 2. In comparison, indium sulphide thin films grown from un-
complexed indium by SILAR method on glass substrate were nanocrystalline with cubic crystal structure
[7].
3
.3. Optical studies
It has been well reported in the literature, that the band gap of In S increases from 2.1 for pure In S to
2
3
2 3
2
.6–2.9 eV in the presence of oxygen. In the present case, optical absorption spectroscopy was utilized to
2
study the optical band gap of indium sulphide thin film. The plot of (ahn) against hn is a straight portion
showing direct optical band gap transition and extrapolating straight line portion at a = 0 gives
E = 2.7 eV (Fig. 2). This value is greater than the value reported earlier (2.1 eV) for pure In S film.
g
2 3
This greater value of the optical band gap can be attributed to the presence of oxygen [1,2] in film
2 3
Fig. 1. XRD pattern of In S thin film deposited on glass substrate.

H.M. Pathan et al. / Materials Research Bulletin 40 (2005) 1018–1023
1021
Table 2
Comparison of observed ‘d’ values with standard ‘d’ values of SILAR grown indium sulphide thin films [9]
˚
Observed ‘d’ values (A)
˚
Standard ‘d’ values (A)
Sr. no.
Plane (h k l)
Phases
In2S3
Crystal structure
1
2
3
4
5
3.48
2.08
1.71
1.46
1.21
3.4740
2.0860
1.7373
1.4831
1.2131
1 0 4
1 2 2
2 0 8
1 3 4
4 1 3
Rhombohedral
Rhombohedral
Rhombohedral
Rhombohedral
Rhombohedral
In
In
2
S
S
3
2
3
In2S3
In
2 3
S
evidenced from RBS study as In S can be considered as a compound originating from a II–VI group by
2
3
replacement of the divalent metal. This produces a defect compound of the formation M X , where the
2
3
sulphide from its crystal structure in which part of cation sites remains empty.
.4. Surface morphological and compositional studies
Scanning electron microscopy (SEM) is a convenient method to study microstructure of thin films.
3
SEM was utilized to study the surface morphology of the indium sulphide thin film. Fig. 3(a) and (b)
shows the SEM images of indium sulphide at two different magnifications 1 KX and 10 KX, respectively.
It is seen from Fig. 3(a) that the film is dense, smooth and homogeneous. From Fig. 3(b) it is concluded
that the film consist of fine grain particles.
2
Fig. 2. Plot of (ahn) against hn for In
2
S
3
thin film.

1
022
H.M. Pathan et al. / Materials Research Bulletin 40 (2005) 1018–1023
Fig. 3. Scanning electron microscopy (SEM) of In S thin film at (a) 1 KX and (b) 10 KX magnifications on FTO coated glass
2
3
substrate.
Fig. 4. RBS spectrum for indium sulphide thin film onto glass substrate.

H.M. Pathan et al. / Materials Research Bulletin 40 (2005) 1018–1023
1023
Fig. 4 displays RBS spectrum for indium sulphide thin films on glass substrate. The observed spectrum
fit well with simulated spectrum which reveals uniform distribution of the indium sulphide film material
on glass substrate. The presence of oxygen could be identified by small peak with edge energy 550 keV.
This is common observation for many chemically deposited chalcogenide thin films from aqueous bath
[2,9].
4
. Conclusions
The deposition of In S is feasible by complexed indium sulphate solution by SILAR method at room
2
3
temperature. The film has rhombohedral crystal structure. The films are nanocrystalline in nature. The
optical band gap was found to be 2.7 eV. The presence of oxygen is detected in RBS analysis.
Acknowledgements
We thank the UGC, New Delhi (India) for the financial support through departmental research scheme
UGC-DRS-SAP: 1999–2004. HMP is thankful to CSIR, New Delhi for the award of Senior Research
Fellowship (SRF).
References
[
[
[
1] N. Barreau, S. Marsillac, J.C. Bernede, A. Barreau, Appl. Surf. Sci. 161 (2000) 20.
2] C.D. Lokhande, A. Ennaoui, P.S. Patil, M. Giersig, K. Diesner, M. Muller, H. Tributsch, Thin Solid Films 340 (1999) 18.
3] R. Bay’on, C. Gullen, M.A. Martiner, M.T. Gutierrez, J. Herrero, in: Proceedings of the 14th European Photovoltaic Solar
Energy Conference and Exhibitions, E.C., Barcelona, Spain, 1997, p. 2050.
[
4] D. Hariskos, M. Ruckh, U. Ruhle, T. Walter, H.W. Schock, J. Hedstrom, L. Stolt, Solar Energy Mater. Solar Cells 41/42
(
5] R. Bay’on, J. Herrero, Thin Solid Films 387 (2001) 111.
1996) 345.
[
[
[
[
[
6] R. Bay’on, J. Herrero, Appl. Surf. Sci. 158 (2000) 49.
7] R.S. Mane, C.D. Lokhande, Mater. Chem. Phys. 78 (2002) 15.
8] ASTM File No.: 33-0624.
9] C.D. Lokhande, A. Ennaoui, P.S. Patil, M. Giersig, M. Muller, K. Diesner, H. Tributsch, Thin Solid Films 330 (1998) 70.