JOURNAL OF MATERIALS SCIENCE LETTERS 18 (1999)1453– 1455
Preparation and characterization of Sb
2
S
3
thin films using a successive
ionic layer adsorption and reaction (SILAR) method
B. R. SANKAPAL, R. S. MANE, C. D. LOKHANDE
Thin Film Physics Laboratory, Department of Physics, Shivaji University, Kolhapur - 416 004, India
Group V-VI compound thin films have potential appli-
cations in optoelectronic devices, photoelectrochemi-
cal devices, thermoelectric coolers, solar selective and
decorative coatings etc. A number of methods have
been employed for the preparation of group V-VI com-
pound thin films. Antimony trisulphide belongs to this
class of materials. It finds some special applications in
the target materials for television cameras, microwave
devices, switching devices and various optoelectronic
devices. Various methods such as vacuum evaporation,
sintering and precipitate and chemical methods have
been employed to prepare Sb
2
S
3
thin and thick films.
The evaporation method results in a non-stoichiometric
composition due to differences in vapour pressures
against the reacting species. Chemical methods have
some advantages for the preparation of films and these
methods do not involve sophisticated vacuum systems
[1–6]. Deposition can be performed on to different
types of substrates such as metals, insulators or semi-
conductors.
The successive ionic layer adsorption and reaction
(SILAR) method is a relatively new and less investi-
gated method, first reported in 1985 by Ristov et al.
[6]. The name SILAR was ascribed to this method by
Nicolau [7] and was discussed in subsequent papers
of Nicolau et al.[8] which dealt with ZnS, ZnCdS and
CdS thin films. In this letter, it is our intention to re-
port interest in the SILAR method as applied to anti-
mony trisulphide thin films. The structural, optical and
electrical properties are carried out for the Sb
2
S
3
thin
films.
The SILAR method is mainly based on immersion of
the substrate into separate cation and anion precursor
solutions rinsing between every immersion with ion
exchanged water to avoid homogeneous precipitation.
The cationic precursor of Sb
2
S
3
was a 0.2 mol l
−1
aqueous solution of antimony trioxide. The pH (∼6) of
the solutionwasadjustedbyusingtartaricacid.Thean-
ionic precursor was 0.4 moll
−1
of sodium thiosulphate
solution.
For the deposition of Sb
2
S
3
thin films, a glass sub-
strate was immersed in a cationic precursor of Sb
2
O
3
(0.2M) for 20 s in which Sb
3+
ions are adsorbed
on the surface of the substrate. Then the substrate
was rinsed with double distilled water (conductivity
∼1 µ
−1
cm
−1
) for 10 s to remove unadsorbed ions.
The substrate was then immersed in an anionic pre-
cursor of Na
2
S
2
O
3
(0.4 M) for 20s in which S
2−
ions
werereactedwithpreviously adsorbed Sb
3+
ionson the
glass substrate. This was followed by rinsing again in
the double distilled water. This completes one cycle of
deposition. Such SILAR-cycles were repeated several
times to form a continuous Sb
2
S
3
thin film on a glass
substrate.Thetemperatureoftheprecursorsolutionwas
maintainedat 50
◦
C(±1
◦
C)using thetemperature con-
troller.
The optimized parameters used for the deposition
of Sb
2
S
3
thin films by the SILAR method onto glass
substrates are summarized in Table I.
Thestructuralcharacterizationoftheantimonytrisul-
phide thin films was carried out from X-ray diffraction
patterns obtained using a Philips X-ray diffractometer,
model PW-1710 (λ =1.5406
˚
A for CuK
α
radiation).
The thickness of the films was determined by a gravi-
metric weight difference method by assuming the bulk
density of Sb
2
S
3
as 4.12 gcm
−3
. Optical absorption
spectra of the films were recorded by using a UV-VIS-
NIR spectrophotometer (Model Hitachi-330 Japan) in
the wavelength range of 350–850nm. Resistivity was
measured by a d.c. two point probe method in the tem-
perature range 300–500 K. Silver paste was applied to
providegoodohmiccontactswithSb
2
S
3
thinfilms.The
area defined was 0.5 cm
2
.
Fig.1shows the variationofthe Sb
2
S
3
filmthickness
with the number of immersions by using an optimized
concentration, pH of the precursors, temperature of so-
lutions and immersion time as shown in Table I. The
film has the maximum terminal thickness of 0.78 µm
for 14 SILAR cycles after which the film starts peeling
off from the glass substrate.
Fig. 2 shows the XRD pattern of the Sb
2
S
3
film de-
posited on the glass substrate. The Sb
2
S
3
film consists
of amorphous or fine grains with an orthorhombic crys-
talstructure. The comparisonofthe observed‘d’ values
with standard ‘d’ values from ASTM data [9] for Sb
2
S
3
is made in Table II. These values are in good agree-
ment confirming that the material deposited onto the
substrate is Sb
2
S
3
. The broad hump in the XRD pattern
TABLE I Optimized parameters forthedepositionofSb
2
S
3
thinfilms
by the SILAR method
Precursor solutions Antimony trioxide Sodium thiosulphate
Concentration (M) 0.2 0.4
pH∼ 66
Immersion rate 14 14
Immersion time (s) 20 20
Temperature (
◦
C) 50 60
0261–8028
C
1999 Kluwer Academic Publishers
1453