Effect of silver doping on spray pyrolysed Indium Sulfide thin films
Mahdi H. Suhail1, Souad G. Kaleel 2 & Faten M.Yasser 2
1
2
Dept. of Physics, College of Science, Univ. of Baghdad-Iraq
Dept. of Physics, College of Science for women, Univ. of Baghdad-Iraq
E Mail:mhsuhail@yahoo.com, mhsuhail956@gmail.com
Abstract:
In this research, Ag-doped In2S3 thin films were prepared by chemical spray pyrolysis
technique, using mixing Indium chloride (InCl3) and thiourea CS(NH2)2, on glass substrates
preheated at (350°C) with spray
rate 5sec / min , with different
doping
(3%,6%,9%,12%,15%) .These films are characterized by structural, optical and electrical
measurement techniques. The investigation of (XRD) indicates that the (In2S3) films are
polycrystalline type of (tetragonal), the effect of increasing the doping was clear in the
crystalline structure of the films by appearance new peak relate to
(103,121,110,111,112,123,) and (120) planes for Ag with Monoclinic phase. The optical
properties such as transmittance spectra of In2S3 film were collected between 300 to 1100nm
wavelength. The optical energy gap (Eg)and the optical constants, which involve refractive
index (n), extinction coefficient (k), real dielectric constant (r) and imaginary dielectric
constant (i) have been studied.
Key words: In2S3thin film, chemical spray pyrolysis, structural, optical properties.
1. Introduction
The substitution of cadmium sulfide (CdS) buffer layer by alternative materials is among
the challenges faced by the researchers working on Cu (In, Ga) (S, Se)2 thin films based solar
cells since the end of 1990s. Due to environmental hazards connected with production and
disposal of CdS layers, much attention has been focused on the development of other buffer
layers. One such possible substitute for CdS is Indium sulfide (In2S3). In2S3 exhibits
different polymorphic structures such as α, β and γ depending on the processing parameters.
β-In2S3 phase is found to be the stable crystalline phase of indium sulfide at room
temperature with tetragonal structure [1-8]. Indium sulfide (In2S3) is an important material
for optoelectronic and photovoltaic applications and is a promising candidate for many
technological applications due to its stability, wider band gap and photoconductive behavior.
It can be used as an effective nontoxic substitute for cadmium sulfide (CdS) in Cu (In,Ga)Se2
based solar cells. This material not only eliminates toxic cadmium but also improve light
transmission in the blue wavelength region on having band gap wider than that of CdS [9-11].
In2S3 is a III–VI compound originating from the II–VI semiconductor by replacing
group II metals by group III elements and exists in three crystallographic modifications α, β
and γ with β -In2S3 being the stable state with a tetragonal structure at room temperature[12,
13]. In this phase, it crystallizes in defect spinel structure with a high degree of disorder and
high degree of vacancies, ordering at tetrahedral cation sites [14]. Due to its high defect
structure, β -In2S3 is an n-type semiconductor with a direct band gap of 1.98 eV finds many
applications in different fields. However, a small fraction of indium atoms may leave their
ordered positions and occupy crystallographically ordered vacancies. This results in a number
of quasi-interstitial cations and an equal number of cation vacancies, so that in a
stoichiometric crystal of β -In2S3, a considerable degree of disorder is always present [15].
The optical properties of thin films are very important for many applications, (such as in
solar cells, optical detectors, and optoelectronic devices, due to high stability [16]), as well as
optoelectronics, integrated optics, solar power engineering, microelectronics, optical sensor
technology and high absorption coefficient [17]. The optical properties of the indium sulfide
films vary between the various studies. The band gap values reported in the literature extend
from 2.0 eV up to 3.7 eV. It should be noted that values of the band gap were determined
assuming a direct allowed transition. Contrary to this assumption, an indirect band gap was
assumed by Rahman and Podder [18] as well as Allsop et al [19] for the ILGAR process.
The aim of the present study is to discuss the possibility of preparing a thin film of
indium sulfate using Chemical Spray Pyrolysis Method with ratio (1.2 :8) and Study the
Structural, Electrical and Optical properties of In2S3 films doped with Ag and see the effect of
doping on those properties.
2. Experiential Details:
The preparation of In2S3 thin films glass slide was carried out using chemical spray
pyrolysis technique , the glass substrates (7.6 x2.6 x0.1)cm were previously cleaned in water
with detergent , then immersed in ethanol to remove any oil , last rinsed with distilled water
and dried in air. The precursor solution prepared by dissolving a certain amount (0.1 M) of
mixing Indium chloride (InCl3) and thiourea CS(NH2)2 as an starting materials, (molecular
weight of the InCl3 = 221.1761 g/mol, molecular weight for CS (NH2)2 = 76.12 g/mol) in
100 ml of distilled water and increase clarity of the solution.
The glass substrate was kept at a temperature of (350°C). The spray rate of (5 s /min) was
maintained using carrier gas is nitrogen compressor regulator (3bar), the distance between
spray nozzle and substrates was fixed at (30 ±1 cm). The deposition process was repeated
several times and reproducibility of the results until we get the required thickness. After
deposition process was completed, the films were kept on the heater at deposition
temperature for 30 min in order to provide sufficient time and temperature for
recrystallization. The In2S3 formulation can be represented as:
2InCl3 + 3 Cs (NH2)2 + 6 H2O
In2S3 + 3 CO2 + 6NH4Cl
The ratio of the compounds in the solution was varied to change the atomic ratio of In and
S in the resulting films. In the present studies the ratio of InCl3 & (CS (NH2)2) was selected to
be (1.2:8) and doping with Ag with (3%, 6%, 9%, 12%, 15%). XRD instrument is (Shimadzu
6000) type with the following specifications are target is CuKα radiation with wavelength,
λ=1.54056A°. The average grain size of thin film samples were calculated by using the
Scherrer's equation [20] .
D=
0.9 𝜆
… … … … … … … … … … … … … … (1)
𝛽 cos 𝜃
where: λ 𝑖s the X-ray wavelength (1.5406Å), 𝛽 is the full width at half maximum (FWHM) in
radian and 𝜃 Bragg ′ s angle.
The In2S3 thin film is a tetragonal structure and the lattice parameter 'a' can be evaluated from the
relation [21]:
1
𝑑2
= [
ℎ2 + 𝑘 2
𝑎2
]+
𝑙2
𝑐2
… … … … … … … … … … …(2)
where: 𝑑 is the interplaner distance , ℎ𝑘𝑙 ∶ miller indices ,𝑎 & 𝑐 𝑖𝑠 lattice constants.
To study the morphological characteristics and surface roughness of In2S3: Ag thin films,
surface morphology photographs were recorded by using (CSPM AA3000 AFM ) supplied
by Angstrom Company .
The spectral transmittance and absorbance of the films were measured by (UV-160A)
UV-Visible recording Spectrophotometer, Japanese company UV/VIS spectrophotometer in
the range (300-1100) nm. In order to determine the optical band gap of the semiconductor,
the following dependence of the absorption coefficient 'α' on the photon energy equation is
used, for direct transitions:
αhν = A (αhν – Eg) r
…………………………(3)
Where, ν is the frequency of the incident photon, h is Planck's constant, A is constant, Eg is
optical energy gap and r is the number which characterizes the optical processes.
3. Results and Discussions:
3-1- structural properties:
Figure 1 represents the X-ray diffraction of the In2S3 thin film at (350°C). It reveals from
the pattern the film is a polycrystalline and the film has a tetragonal structure according to
ASTM card.
Fig. (1): X-ray diffraction pattern for pure In2S3 film deposited by spray paralysis at
substrate temperature at Ts= (350 ºC).
The results compared with ASTM card were in a good agreement as shown in table 1.
Table (1) lists the observed the d-values with standard (JCPDS-ICDD file NO, 96-400-0814
for In2S3.
Table (1) X-ray diffraction pattern data with standard card for pure In2S3 film.
FWHM dhkl Exp
G.S
dhkl Std
2θ (Deg.)
hkl
phase
card No.
(Deg.)
(Å)
(Å)
(Å)
27.40
0.60
3.252
128
3.2497
(213)
Tet. In2S3
96-400-0814
33.31
0.64
2.688
122
2.6943
(220)
Tet. In2S3
96-400-0814
43.62
0.70
2.073
115
2.0741
(323)
Tet. In2S3
96-400-0814
47.75
0.76
1.903
108
1.9060
(22 12) Tet. In2S3
96-400-0814
59.39
0.70
1.555
123
1.5560
(04 12) Tet. In2S3
96-400-0814
The XRD patterns of the as deposited In2S3: Ag films on glass at substrate temperature
equal to 350°C with thickness equal to 0.333 m, for different doping (3%, 6%, 9%, 12%,
and 15%) are illustrated in Figure 3.
From XRD studies (Figure 2, the effect of increasing the doping was clear in the crystalline
structure of the films by appearance new peak relate to (103, 121, 110, 111, 112, 123,) and
(120) planes for Ag with Monoclinic phase. It was also clear that after diffusion of silver the
peak positions shifted slightly to lower values of 2θ. Correspondingly, value of lattice
spacing (d) increased, (Table 2).
Fig. (2 X-ray diffraction pattern for In2S3 film doped with different Ag content (a=3%,
b=6%, c=9%, d=12%, e=15%) deposited by spray paralysis.
The d-values of all samples coincided with that of β-In2S3 in standard JCPDS data card
(96-900-0254). For silver doped samples, it was very clear that the Bragg peaks in XRD
pattern became more intense, indicating a clear improvement in crystallinity. The observed
d-values with standard (JCPDS-ICDD file NO, 96-400-0814, and 96-900-0245) for In2S3
compound. The observed of the d-values for In2S3: Ag for different doping (3%, 6%, 9%,
12%, and 15%) is in agreement with the standard values for the tetragonal structure. Grain
size calculated using Debye Scherrer formula, the Grain size for (213) plane is (256.8, 428)
increases with doping with (3%,6%) and for doping with (9%,12%,15%) the Grain size
(427.9,233.3,307.7)decreases with increases doping, Our result are nearly in agreement with
Meril Mathew[22]. The XRD pattern shows the appearance of new preferred plane for
crystal growth localized at 2θ =29.10, 29.21, 28.99, 29.05o,corresponding to (111) for Ag2S
which affirm that addition of Ag to the In2S3 binary system has been done successfully
where (Ag) atom become bounded with it[23,24].
Generally from the XRD spectrum, the Full-width at the half maximum (FWHM) of the
diffraction peak is smaller, the grain size of thin film was larger and the quality of the film
was better. It proved that the crystalline quality of In2S3 thin film obtained in experiment was
better.
3.2. Morphological properties of pure (In2S3) and (In2S3: Ag thin films
The grain size (grain diameter) and average roughness and root mean square roughness
(RMS) of pure In2S3 and In2S3:Ag thin films for different doping (3%,6%,9%,12%,15%)
deposited on glass substrates with substrate temperature(350°C) and thickness(0.333) µm have
been measured using AFM Figure 4 and the results listed in table 3.
pure
a
b
c
d
e
Fig. (4 ): AFM image for pure(In2S3), )and ( In2S3:Ag ) thin films at(0.333µm) with
difference doping(a=3%, b=6%, c=9% , d=12% , e=15%).
Table (3) show the value of average roughness and root mean square roughness (RMS)
and average grain size for In2S3: Ag.
Table (3) the value of average roughness, RMS and average grain size for In2S3:Ag
Doping Ag %
average roughness
(nm)
RMS
(nm)
average grain size
(nm)
3%
0.849
1.02
-
6%
1.15
1.37
-
9%
3.06
3.73
104.41
12%
0.825
1.04
61.53
15%
0.445
0.559
98.32
It is observed from this table that the average roughness and root mean square roughness
value increasing with increase the doping for doped with Ag (3%,6%,9%). While the average
roughness for films doped with Ag (12%, 15%) decreasing with increase doping. On the
other hand from the same table the average of grain size decreases with increasing of doping,
i.e this decrease but in non systematic sequence with the increase of Ag content, this behavior
can be explained on the basis that addition of Ag to In2S3 binary system reduces the local
structure since it leads to some degree of disordering [Revathi et al 2008 [21] and Mathew et al
2010 [22] ].
3-3- Optical Properties:
In2S3 thin films were successfully deposited on glass substrate using chemical spray
deposition technique with thickness 250 nm. The films are firmly adhered to the substrates.
3.3.1. The Transmittance Spectra of doped In2S3 thin Films
The transmittance spectrum of as-deposited In2S3: Ag thin films, where doping equal to
(3%, 6%, 9%, 12%, 15%), are shown in figure 4.
100
Ag= 3%
Ag= 6%
Ag= 9%
Ag=12%
Ag=15%
Transmittance%
80
60
40
20
0
300
400
500
600
700
λ (nm)
800
900
1000
1100
Fig. (4) The transmittance spectra for (In2S3:Ag) at Ts=350°C.
From figure (4), it can be seen that all In2S3 films deposited at different doping having a high
transparency in visible region, while the transparency in UV region was very low. All spectrums
reveal very pronounced interference effects for photon energies below the fundamental
absorption edge by exhibiting an interference pattern. Such behavior of the spectrum is evidence
of the thickness uniformity of the films.
We notice also that the transmittance decreases but not uniform with increasing of doping
and shifted to longer wavelengths. This may be attributed to the creation levels at the energy
band by increasing doping. It is observed that maximum transmittance at (3%) doping for
wavelength range (300-900 nm) i.e. at visible region which is very suitable for solar cell.
However, transmittance is inversely proportional with doping, i.e., it decreases when doping
increases, transmittance decreases slightly with the increasing of film doping. This behavior is
attributed to the increase the number of atoms with the doping that leads to the increase of the
number of collision between incident atoms, which in turn, leads to the increase of absorbance
and decreasing transmittance.
3.3.2 Absorbance spectrum:
The absorbance spectrums of as-deposited In2S3: Ag thin films, for doping equal to (3%,
6%, 9%, 12%, 15%), are shown in figure 5.
4
Ag= 3%
3.5
Ag= 6%
Absorbance
3
Ag= 9%
2.5
Ag=12%
2
Ag=15%
1.5
1
0.5
0
300
400
500
600
700
λ (nm)
800
900
1000
1100
Fig. (5) The absorbance spectra for In2S3:Ag at Ts=350°C.
It is clear that as the Ag doping increases the absorbance of thin films increases. This increase
in the absorbance is attributed to the increase of Ag concentration (Sulfur vacancies increase)
which leads to the increase of the depth of donor levels, which had been deduced from the
electrical measurements, as will be discussed later. These donor levels are associated with these
vacancies and will be available for the photons to be absorbed. Therefore the absorbance will
increase with the increase in Ag concentration .As well as from the same figure, it can be seen
that the absorption edge shifts to the higher wavelengths. From this shifting in the absorption
edge to the red region it can be deduced that the energy gap of In2S3: Ag thin films will decrease
with the increase in (Ag) as will be discussed later.
3.3.3 Absorption Coefficient:
α (cm-1)x 100000
The absorption coefficient () was determined from the region of high absorption at the
fundamental absorption edge of the film. The variation of the absorption coefficient of (In2S3:
Ag) thin films with the wavelength for doping equal to (3%, 6%, 9%, 12%, 15%) is shown in
figure 6.
4
3.5
3
2.5
2
1.5
1
0.5
0
Ag= 3%
Ag= 6%
Ag= 9%
Ag=12%
Ag=15%
300
400
500
600
700
800
λ (nm)
900
1000
1100
Fig. (6) The absorption coefficient spectra for (In2S3:Ag) at Ts=350°C.
We can notice that  in general decreases with increasing of wavelength, () has the same
behavior of the absorbance and in order of (104) cm-1 which supports the direct band gap nature
of the semiconductor. It is also clear that the absorption coefficient of thin films increases with
the increase in Ag concentration. The higher values of the absorption is attributed that the
incoming photons have the sufficient energy to excite the electrons from the valence band to the
conduction band .The absorption decreases in the higher wavelength region and this decrease is
corresponds to the reduction in the photon’s energy
3.3.4. Extinction coefficient:
Figure 7 illustrates the variation of the extinction coefficient of In2S3: Ag thin films with
the wavelength for doping equal to (3%, 6%, 9%, 12% & 15%).
It can be noted that (k)
varies with the increase in the wavelength corresponding to the reduction in the photon’s
energy. The increases highly at the absorption edge region. This increase is attributed to the
increase of the absorption coefficient due to the direct electronic transitions . Later (k)
reaches its maximum value at the high absorption region corresponding to the increment in
the photon’s energy and the increase in the absorption coefficient with the decrease in the
wavelength.
0.8
0.7
0.6
0.5
k 0.4
0.3
0.2
0.1
0
Ag= 3%
Ag= 6%
Ag= 9%
Ag=12%
Ag=15%
300
400
500
600
700
800
λ (nm)
900
1000
1100
Fig.(7): Extinction coefficient as a function of wavelength for In2S3:Ag thin films .
3.3.5. Refractive Index:
It is necessary to give attention to the refractive index (n) in order to complete the
fundamental study of the optical properties and the optical behavior of the material .The variation
refractive index of In2S3: Ag thin films as a function of the wavelength is illustrated in figure 8.
8
7
6
5
n 4
3
2
1
0
Ag= 3%
Ag= 6%
Ag= 9%
Ag=12%
Ag=15%
300
400
500
600
700
800
λ (nm)
900
1000
1100
Fig.(8):The variation of the refractive index as a function of the wavelength for (In2S3:Ag)
thin films at Ts=350°C.
It is clear from this figure that the refractive index decreases with the increase in the
wavelength of the incident photon. Also it can be observed, that the refractive index of In2S3: Ag
thin films increases with the increase in the doping. This increase is attributed to the increase in
the grain size of the films with the increase in the Ag concentration, which intern causing an
increment in the compactness of the films which intern reduces the speed of light in the material
of the thin film and then leads to an increase in the refractive index.
In addition, it can be observed that the curves of the refractive index shifts to the higher
wavelength with the increase in the Ag concentration due to the increasing in the absorption
coefficient and the decrease in the optical energy gap films. The increase may be attributed to
higher packing density and the change in crystalline structure, this increase due to the
enhancement of growth crystalline.
3.3.6. Optical Energy Gap:
In order to determine the optical band gap, graph was plotted with (αhν)2 against hν.
Optical band gap was determined from this plot for all films by the linear fit in the straight
portion of the graph. The relations are drawn (figure 9) between (αhν)2 and photon energy
( hν) illustrate allowed direct transition electronic .
100
90
80
70
60
50
40
30
20
10
0
(αhν) 2 (cm -2. (eV)
2)*1010
Ag= 3%
Ag= 6%
Ag= 9%
Ag=12%
Ag=15%
1
2
3
4
5
hν (eV)
Fig. (9) The plot of (ahν)2 vs. hν for (In2S3:Ag) at Ts=350°C.
From figures 9, it can be observed that (Eg) is decreasing slightly with the increasing of
doping and shifts towards the red region as the Ag concentration in the films increases for all
films. The optical energy gap values for In2S3: Ag thin films were 3.35 eV, 3.10 eV, 2.50 eV,
2.30 eV and 2.20 eV for doping equal to (3%, 6%, 9%, 12% & 15%) respectively. This is
because of the increasing in the carrier concentration, which results in filling the bottom of the
conduction band that leads to the decrease in hole between (C.B.) levels and (V.B.) level that
leads to zoom out the energy gap band [25] and may be attributed to the decrease of S
concentration (Sulfur vacancies increase) which leads to an increase of the depth of donor levels
associated with these vacancies which in turn cause a reduction in the optical energy gap for
In2S3:Ag thin films . The obtained values of the optical energy gap match well with the reported
values of In2S3.
3.3. 7. Dielectric Constant:
Figure 10, 11 illustrates the variation of the real (εr) and imaginary (εi) parts of the
dielectric constant as a function of the wavelength for In2S3: Ag thin films for doping equal to
(3%, 6%, 9%, 12% & 15%).
The real part of the dielectric constant (εr) depends mainly on the value of (n2), because of the
smaller values of (k 2) comparison with (n2), whereas the imaginary part of the dielectric
constant (εi) depends mainly on the (k) values which are related to the variations of the
absorption coefficient. It is observed that their values increase with wavelength to maximum
value of (εr) and then decrease for doping (3%, 6%), but for the rest doping (9%, 12%, 15%)
continue to increase slightly.
6
Ag= 3%
Ag= 6%
Ag= 9%
Ag=12%
Ag=15%
5
4
εi
3
2
1
0
300
400
500
600
700
λ (nm)
800
900
1000
1100
Fig.(10):The variation of the real part of the dielectric constant as a function of the
wavelength for In2S3:Ag thin films.
50
45
40
35
30
εr 25
20
15
10
5
0
Ag= 3%
Ag= 6%
Ag= 9%
Ag=12%
Ag=15%
300
400
500
600
700
800
900
1000 1100
λ (nm)
Fig.(11):The variation of the imaginary part of the dielectric constant as a function of the
wavelength for In2S3 :Ag thin films .
The optical properties parameters including absorption coefficient and optical
constants which include refractive index, extinction coefficient, real and imaginary parts of
the dielectric constant at the wavelength which is equal to (600) nm for (In2S3:Ag)thin films,
for doping equal to (3% , 6%,9% , 12% & 15%) deposited by chemical spray pyrolysis
method on a glass substrate at 350°C with thickness 250 nm are listed in table (4 ) .
Table (4): The optical properties parameters of (In2S3: Ag) thin films at (λ=600) nm
Ag%
T%
α (cm-1)
K
n
εr
εi
Eg (eV)
3
6
9
12
15
37.15
32.36
22.36
14.45
11.75
39612
45139
59929
77381
85672
0.189
0.216
0.286
0.370
0.409
4.119
4.380
4.902
5.203
5.244
16.932
19.135
23.947
26.937
27.334
1.559
1.889
2.807
3.847
4.292
3.350
3.100
2.500
2.300
2.200
It is clear from this table that all these parameters increase with the increase in the
doping except Eg and Transition.
3.4. The Electrical Properties of thin films
The electrical properties of (In2S3:Ag) thin films include the D.C. conductivity from
which the transport mechanism of the charge carriers can be estimated, and the Hall effect
which gives information about the type, concentration and mobility of the charge carriers.
The (d.c) conductivity (σd.c) for In2S3: Ag films has been studied as a function of (1000/T)
with the range of (398-443 K), at different value of doping (3%, 6%, 9%, 12%, 15%). The
activation energy deduced from the figure ,the type of charge carriers, concentration (nH) and
Hall mobility (H) for thin films, have been calculated from Hall coefficient (RH) data and D.C
conductivity are listed in Table (5).
Table (5): D.C. conductivity parameters for In2S3:Ag films at different doping, with
thicknesses250nm and substrate temperatures350°C.
Doping
with
(Ag %)
Ea1 (eV)
Ea2 (eV)
(298-73)K
(373-43)K
pure
In2S3
0.746
0.520
3%
0.198
nH
cm -3
1.345 x1014
0.560
0.212
0.389
0.157
.cm-1
1.482 x 10-3
76.55
4.920 x 10-9
13.793x10-3
0.198
7.045
1.742 x 10-1
0.368x10-3
0.129
160.1
1.075 x 10-2
232.018x10-3
0.187
4.432 x1013
15%
σR.T
0.727x10-3
3.972 x1013
12%
69.17
0.137
1.526 x1017
9%
R.
.cm-1
2.010x10-3
4.459 x1010
6%
H
2
cm / V.s
470.1
4.099 x 10-4
3100.77x10-3
0.013
2.383 x1015
544.4
1.583 x 10-2
The conductivity of In2S3 and In2S3:Ag films with 250nm thick are n-type as confirmed
by Hall Effect measurements. Our results agree with Teny et al.[25] , Mathew et al.[22] and Kumar
et al.[26] .
The two conduction mechanisms mean that the conductivity is non-linear with temperature
. The first activation energy (Ea1) occurs at low temperatures , in which the conduction
mechanism is due to charge carriers' transport (hopping) to localized states near the conduction
[27]
band[6,23] . In this temperature region , the temperature dependence of conductivity for all ratio of
(doping)increases with small activation energies equal to(0.198 , 0.560 , &0.389 ) eV for doping
equal to (3%,6% ,12%) respectively and decreases with small activation energies equal to (0.212
,0.157 ) for doping equal to (9%,15%) respectively. The second activation energy (Ea2) occurs at
high temperatures, in which the conduction mechanism is attributed to the thermal excitation of
charge carriers from grain boundaries to neutral region of the grains [6]. It is specifically due to
carriers excited into the extended states beyond the mobility edge [7].In this temperature region,
activation energies was equal to (0.137 , 0.198 & 0.187 ) eV for doping equal to (3%,6%,12%)
respectively and decreases with activation energies equal to(0.1299,0.0130) eV for doping equal
to (9%,15%) respectively.
This increases is expected because the energy gap of In2S3:Ag thin films decreases with the
increase in the Ag concentration , which requires lower energies .Besides the decrease in the
activation energies is attributed to the increase in the grain size of In2S3:Ag thin films as the Ag
concentration increases which causes an improvement in the crystallinity and homogeneity of
In2S3:Ag thin films, which are evident from the XRD analysis of In2S3:Ag thin films.
Since the activation energy represents a mean value of the inter-crystalline barrier height
combining the effects of both carrier concentration and mobility, it is expected that the measured
values of the activation energy will differ among researchers using different preparation
conditions [5].
4. Conclusions:
The homemade chemical spray pyrolysis unit has been used to prepare In2S3 thin films.
The dependences of structural, optical and electrical properties of In2S3 thin films were
investigated on increase doping varied from 3% to 15%. The XRD results showed peaks
corresponding to the pure In2S3 films were observed, indicating that shift in the peak
positions. The transmittance is generally low with increase doping in VIS region, this
behavior converse with absorbance which was increased. Allowed direct energy band gap
transitions were the most probable transition, and were found to vary from (3.35-2.2)eV for
(3%-15%) respectively obtained for the In2S3 film under various doping. Values of the
refractive index and extinction coefficient were increase within range (2.5-5.2) and (0.079.0409) respectively with various doping. The conductivity of In2S3 and In2S3: Ag films are ntype as confirmed by Hall Effect measurements. The activation energy represents a mean
value of the inter-crystalline barrier height combining the effects of both carrier concentration
and mobility. The two conduction mechanisms mean that the conductivity is non-linear with
temperature
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