Wide Band Gap CuI Thin Film through SILAR Technique: Optimization
of Deposition Technique
P.K.Sheela
Department of Physics, Sree Narayana College, Chelannur, Kerala
Abstract
Deposition parameters play an important role in determining the properties of
semiconducting thin films. Copper iodide thin films were deposited at room temperature on
the glass substrates by a simple SILAR method under different dipping intervals in cationic
and anionic precursors. X-ray diffraction studies of as-deposited CuI thin films indicates that
the as-prepared samples were polycrystalline with continuously increasing intensity peak on
enhancing dipping time. The preferential orientation was along (111) direction. The
experimentally observed d- values were compared with JCPDS data for various samples.
These were in good agreement with the standard‘d’ values. The grain size calculations were
also done.
1. Introduction
Cuprous iodide (CuI) has attracted a great attention, as it is a versatile candidate in
optoelectronic devices. Depending on synthesis method and the deposition parameters, there
is variation in the physico-chemical properties of the material. The most interesting nature of
this compound is that, it is an inorganic semiconductor and its coordination chemistry lets it
readily couple with many inorganic and organic ligands as well. CuI belongs to the I–VII
semiconductors with Zinc-blende structure,mainly used in electronic devicessuch as liquid
crystal displays, photovoltaic devices, photothermalcollectors and so on [1-2]. Deposition of
CuI on Cu-tape/n-CuInS2 at roomtemperature by the successive ionic layer adsorption and
reaction(SILAR) technique and study of the influence of wet chemicaliodine treatment is
reported by Sankapal et al. [3]. Further, thechemical bath deposition and SILAR method is
employed bySankpal et al. to obtain the CuI and CuSCN thin films for solar cell windows
application [4]. Thin film preparation by successiveionic layer adsorption and reaction
(SILAR) is simple, lessexpensive, room temperature synthesis and is convenient forlarge area
deposition. Also, SILAR can be used to deposit compound materials on a variety of
substrates such as insulators,semiconductors, metals [5].
In the present research work, we report the synthesis and characterization of copper
iodide thin film deposited on glass substrate by successive ionic layer adsorption and
reaction(SILAR) method at room temperature by changing the dipping time and keeping
rinsing time constant and vice versa. The obtained results regarding crystal structure,
crystallographic orientation,crystallinity etc.for the CuI films under different dipping times
were compared
2. Experimental
Prior to the deposition of CuI thin films, the substrates were cleaned in order to get
uniform deposition. All the reagents used were of analytical grade. We used CuSO4 (0.1
mol/dm3) solution complexed by Na2S2O3 (0.1 mol/dm3 )as a cationic precursor. These two
solutions form a complex thiosulphato cuprate. The release of Cu++ ions is possible via the
following reaction
CuS2O3Cu++ + S2O3--.
In the first set of samples, The rinsing time in water was fixed as 5 sec and number of
SILAR cycles was fixed as 150.The dipping time in solution was varied from 4 sec to
10sec.Water was replaced after each 10 cycles. The frequency of replacement of water was
increased as dipping time in solution was increased. The samples were named as Cu4s
5w,CuI 5s 5w,CuI 6s 5w, CuI 7s 5w,CuI 8s 5W,CuI 9s 5w, CuI 10s 5w and CuI 15s 5w. In
another set of samples dipping time in solution was fixed as 10 sec and rinsing time in water
was varied from 4 sec to 8sec.In this also water was replaced after each 10 cycles. The
samples were named as CuI 10s 4w,CuI 10s 5w,CuI 10s 6w, CuI 10s 7w, andCuI 10s 8w.
.The samples were further characterized for structural properties. Structural studies
were carried out using an X- ray diffractometer (Bruker AXS-8 advance) with CuK
radiation of wavelength 1.5406 Å as the source.
3. Results and discussion
3.1. Structural studies
In Fig. 3.1 and 3.2 the XRD spectra of CuI deposited on glass substrate under
different dipping time is presented. In Figure 3.3, XRD pattern of CuI 10S 5W for which the
most intense peak (2500 arb. Unit) obtained is separately shown. The observed inter-planer
distance ‘d’, is compared with JCPDS data which is in good agreement with the standard ‘d’
values. The lattice parameter is found to be 6.034A˚ . Different peaks of g-CuI corresponding
to planes (1 1 1), (2 2 0) and(3 1 1) of face-centered cubic structure have been identified with
a preferential orientation of (111plane). The presence of a number of peaks in XRD pattern is
the indication of polycrystalline nature of the CuI. The intensity peak increases with increase
in dipping time in solution. The grains size obtained were in the range of 11.75nm to
16.77nm. comparatively high grain size were obtained for samples having greater dipping
time in solution and lower rinsing time in water.
FIGURE
Fig.1. The XRD pattern of CuI thin films—(a)---sample name—(b)-------- and--------
4. Conclusions
A very simplistic method, SILAR, is used for deposition of CuI thin films on glass
substrates. The enhancement in the properties of CuI like adhesion,thickness,crystallinity etc.
is observed on enhancing the dipping time. From XRD pattern the material is confirmed to be
polycrystalline gamma phase CuI with face-centered cubic structure
Acknowledgements
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[3] B.R. Sankapal, A. Ennaoui, T. Guminskaya, Th. Dittrich, W. Bohne, J. Rfhrich, E.Strub,
M.Ch. Lux-Steiner, Thin Solid Films 480 (2005) 142.
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451(2004) 128.
[5] H.M. Pathan, C.D. Lokhande, Bull. Mater. Sci. 27 (2004) 85.