The annealing effect on structural, optical and photoelectrical properties of CuInS2/In2S3 films

Article abstract of DOI:10.1016/j.physb.2011.04.027

Successive Ionic Layer Adsorption and Reaction (SILAR) technique was used to deposit the CuInS₂/In₂S₃ multilayer thin film structure at room temperature. The as-deposited film was annealed at 100, 200, 300, 400 and 500 °C

Full text of DOI:10.1016/j.physb.2011.04.027

Physica B 406 (2011) 2953–2961
Contents lists available at ScienceDirect
Physica B
journal homepage: www.elsevier.com/locate/physb
The annealing effect on structural, optical and photoelectrical properties of
CuInS2/In2S3 films
Mutlu Kundakc-ı n
Atatu¨rk University, Art and Science Faculty, Department of Physics, Erzurum, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Successive Ionic Layer Adsorption and Reaction (SILAR) technique was used to deposit the CuInS2/In2S3
multilayer thin film structure at room temperature. The as-deposited film was annealed at 100, 200,
300, 400 and 500 1C for 30 min in nitrogen atmosphere and the annealing effect on structural, optical
and photoelectrical properties of the film was investigated. X-ray diffraction (XRD) and optical
absorption spectroscopy were used for structural and optical studies. Current–Voltage (I–V) measure-
ments were performed in dark environment and under 15, 30 and 50 mW/cm2 light intensity to
investigate the photosensitivity of the structure. Also, the electrical resistivity of the film was
determined in the temperature range of 300–470 K. It was found that annealing temperature drastically
affects the structural, optical and photoelectrical properties of the CuInS2/In2S3 films.
Received 9 March 2010
Received in revised form
18 February 2011
Accepted 14 April 2011
Available online 21 April 2011
Keywords:
SILAR
Annealing
CuInS2/In2S3
Thin film
& 2011 Elsevier B.V. All rights reserved.
1. Introduction
For CuInS2, with the same buffer layer, efficiency has been
achieved up to 11.4% [17]. Other materials such as ZnO, ZnSe,
CuInS2 can be used to reach high conversion efficiencies due to
its large absorption coefficient and direct band gap of 1.5 eV,
which means it absorbs most of the solar spectrum [1]. Various
techniques have been developed for the preparation of CuInS2
films such as elemental chemical vapor deposition [2], sulfuriza-
tion of metallic precursor [3], spray pyrolysis [4], electro-deposi-
tion [5], co-evaporation [6], chemical bath deposition (CBD) [7]
and chemical route [8]. CuInS2/In2S3 thin films are used for
photovoltaic applications. Most of the efficient CuInS2-based solar
cells were prepared using CdS as the buffer layer [9–13]. Best
efficiency has been found to be 12.5% (active area efficiency) for
the CuInS2/CdS/ZnO cell configuration with MgF2 antireflection
coating reported by Klaery et al. [14]. Recently, many researchers
have focused on the effective replacement of CdS. The motivation
behind this is not only to eliminate toxic cadmium but also, to
improve light transmission in the blue wavelength region by
using a material having band gap wider than that of CdS. One
such possible replacement of CdS is In2S3. In2S3 thin films are the
effective materials as a window layer for the solar cell structures,
because of its a wide and direct band-gap. The wide band gap
(42.5 eV) of In2S3 thin films suggests that it can act as a better
buffer layer than CdS having a band gap of 2.4 eV [15]. Conversion
efficiency has been achieved up to 15.7% with cadmium-free
Inx(OH,S)y as buffer layer for a Cu(In,Ga)Se2-based solar cell [16].
Zn (Se,O), In2S3 and InSe were also used as alternatives to CdS
with considerable conversion efficiencies [18–22].
The aim of this study is to examine and the effect of annealing
on structural, optical and photoelectrical properties of CuInS2/
In2S3 films and improve the crystal quality of CuInS2. The results
of the experiments support this aim. In the present paper, the
CuInS2 thin film used for the photovoltaic applications was grown
by the SILAR method. In order to improve the crystal quality of
CuInS2, it was annealed at different temperatures and grown onto
the In2S3 crystal film instead of amorphous glass substrate. Since
indium was evaporated from the films as a result of annealing, to
support decrease in the amount of indium, CuInS2 film was grown
on the In2S3 films. Besides, there is a lattice match between
CuInS2 and In2S3, so CuInS2 films have a better crystal quality than
those grown on other substrates. Its structural, optical and
photoelectrical properties were investigated as a function of
annealing temperature.
2. Experimental details
Semiconductor thin films can be fabricated by several methods
used both in gas and in liquid phases. In comparison with gas
phase methods, liquid phase methods have some advantages of
providing thin films for large area at low cost but, they lead to
imprecise control of the crystal film structure. One of the liquid
phase methods for deposition of thin films is the SILAR method.
The SILAR method was developed by Nicolau [23] for the
n Tel.: þ90 442 231 4074; fax: þ90 442 236 0948.
E-mail address: mutlu.kundakci@gmail.com
0921-4526/$ - see front matter & 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.physb.2011.04.027

2954
M. Kundakc-ı / Physica B 406 (2011) 2953–2961
400
380
360
340
320
300
280
260
240
220
200
400
As-deposited
Annealed at 1000C
380
360
340
320
300
280
260
240
220
200
180
20
20
20
25
30
35
40
45
50
55
60
50
55
20
25
30
35
40
45
50
55
60
50
60
2θ (degrees)
2θ (degrees)
750
700
650
600
550
500
450
400
350
300
250
1200
1100
1000
900
800
700
600
500
400
300
200
*(112)
Annealed at 300°C
*CuInS2
#In2S3
Annealed at 200°C
*(112)
*CuInS2
#(440)
*(200)
25
30
35
40
45
20
25
30
35
2θ (degrees)
40
45
2θ (degrees)
2100
1950
1800
1650
1500
1350
1200
1050
900
22500
20000
17500
15000
12500
10000
7500
5000
2500
0
*(112)
Annealed at 500°C
&CuS
Annealed at 400°C
*CuInS2
&(110)
#In2S3
#(440)
*(200)
750
600
450
&(025)
300
25
30
35
40
45
50
20
25
30
35
40
45
50
55
2θ (degrees)
2θ (degrees)
Fig. 1. XRD patterns of as-deposited thin films annealed at 100, 200, 300, 400 and 500 1C.

M. Kundakc-ı / Physica B 406 (2011) 2953–2961
2955
deposition of zinc and cadmium chalcogenides thin films 25 years
films was found via the absorption measurements using
a
PerkinElmer UV/VS Lambda 2S Spectrometer with a wavelength
resolution better than 73 nm at room temperature. All electrical
measurements were performed with two steps. In the first step, in
order to investigate photoelectrical properties of CuInS2/In2S3, I–V
measurements were done in dark environment and under 15, 30
and 50 mW/cm2 light intensity. CuInS2/In2S3 thin films were
illuminated by different three tungsten lamps (Philips 230 V,
150 W, 300 W and 500 W). To prevent heating of samples from
tungsten lamp, digital temperature controller (Lake Shore) based
on PT-100 sensor of accuracy 71 1C was used and the tempera-
ture of sample was set to room temperature. Secondly, the
ago. In this method, thin films are fabricated by dipping into two
different solutions of each precursor ion for compound semicon-
ductors. Therefore, the control of the film thickness becomes
feasible by changing the number of the dipping cycles. Further-
more, atomically controlled multilayer thin films or super lattices
can possibly be fabricated by changing precursor solutions. Since
the SILAR method depends only on immersing the substrate into
the solutions, the deposition of films with a large area can be
achieved at low cost.
The glass substrate materials were cleaned with acetone and
water–ethanol (50:50) solution in an ultrasonic bath and dried with
nitrogen. For the deposition of the In2S3 thin film, 0.1 M indium
trichloride (InCl3) solution (pHꢀ5.5) was used as the cationic
precursor and 0.05 M Na2S solution (pHꢀ11.5) as the anionic
precursor. The well-cleaned glass substrate was immersed in the
cationic precursor solution (InCl3) for 30 s in order to adsorb the
indium ions on the surface of glass substrate. Then, the substrate
was rinsed doubly in distilled water for 50 s to prevent homogenous
precipitation. It was followed by immersion in the anionic precursor
solution Na2S (pHꢀ12) for 30 s. Sulfide ions react with the adsorbed
indium ions on the glass substrate resulting in the formation of In2S3
layer. The substrate was rinsed doubly in distilled water for 50 s.
This was the last step for one SILAR cycle. The thicknesses of the
films were calculated within the limit of experimental errors by
using the optical interference method [24]. It was seen that the
thicknesses are increasing with number of SILAR deposition cycles. It
was found that the optimum SILAR cycle is 75 from the absorbance
and XRD measurements. Thus, SILAR cycle was repeated 75 times
and In2S3 layer film was grown at room temperature (27 1C). The
thickness of the films has been calculated as 330714 nm. After
then, the CuInS2 film was grown onto the In2S3 film. CuCl2 ꢁ 2H2O,
InCl3 and Na2S were used in the deposition of the CuInS2 thin film.
The mixed cationic precursor solutions consist of cupric chloride and
indium chloride as the reagents, whose pH value was adjusted to
5.5 by using hydrochloric acid. The source of sulfur ions was
0.05 mol/L Na2S (pHꢀ12). The prepared solutions were percolated
and taken into 100 mL beakers before deposition.
electrical resistivity (r) of the films deposited with different
annealing temperatures has been measured in the temperature
range 300–470 K by the two dc probe method. All I–V measure-
ments were performed by the Keithley 2400 source meter and
Keithley 487 Pico-ammeter.
3. Result and discussion
3.1. XRD analysis
Fig. 1 provides the comparison of typical XRD spectra for CuInS2
thin films annealed at different temperatures. As shown in
Fig. 1(a) and (b), both as-deposited and annealed films at 100 1C
Table 1
d values and (h k l) miller indices of annealed CuInS2/In2S3 thin films for different
annealing temperatures.
Annealing
temperature
(1C)
2
h
(deg.)
hkl
˚
˚
d (A)
d (A)
Observed
Observed
Standard
200
300
27.81
27.81
32.57
48.25
27.81
32.57
48.25
38.41
44.61
3.205
3.205
2.747
1.885
3.205
2.747
1.885
2.338
2.029
3.196
3.196
2.762
1.905
3.196
2.762
1.905
2.308
2.029
112 (CuInS2)
112 (CuInS2)
200 (CuInS2)
440 (In2S3)
112 (CuInS2)
200 (CuInS2)
440 (In2S3)
025 (CuS)
400
500
The deposition was carried out at room temperature (27 1C).
There are four steps in one cycle dipping:
110 (CuS)
(1) The substrate was immersed in the mixed cation precursors
for 30 s.
(2) The substrate was rinsed with doubly distilled water for 50 s
to remove the unattached ions.
(3) The substrate was immersed in 0.05 mol/L sodium sulfide
solution for 30 s.
(4) The substrate was rinsed with doubly distilled water for 50 s
to remove the unreacted ions.
55
50
45
40
35
30
25
Grain Size
The adsorbed Cu2þ and In3þ ions on the substrate react with
the S2ꢂ ions in anion precursor solution to form the sulfide
compound of CuS and In2S3 according to Eqs. (1) and (2). By
repeating such SILAR deposition cycle 75 times, CuInS2/In2S3 thin
film was grown. The reaction for the formation of stoichiometry
CuInS2 is given in Eq. (3).
CuCl2þNa2S-CuSþ2NaCl
2InCl3þ3Na2S-In2S3þ6NaCl
2CuSþIn2S3-2CuInS2þS
(1)
(2)
(3)
200
250
300
350
400
450
500
The as-deposit film was annealed at 100, 200, 300, 400 and
500 1C for 30 min in Nitrogen atmosphere. For structural studies,
Annealing Temperature (°C)
˚
a Rigaku 2200D/Max, X-ray diffractometer of Cu K
radiation with 2
a
(
l
¼1.5405 A)
Fig. 2. Grain size values versus annealing temperature for annealed CuInS2/
y
of 20–701 was used. The band gap value of the
In2S3 films.

2956
M. Kundakc-ı / Physica B 406 (2011) 2953–2961
have an amorphous structure. As the film annealed at 200 1C, the
found peak is reported as the characteristic peak for CuInS2 with the
CuS thin films. Since CuInS2, In2S3 and CuS thin films have some
defects, such as crystallite boundary discontinuities, lattice mis-
match and strain effects; the observed ‘d’ values are a little
different from standard ‘d’ values as seen in Table 1.
The crystallite size of thin films is calculated using Scherer’s
formula:
preferred orientation of (1 1 2) at 2
increasing the annealing temperature from 200 to 300 and 400 1C,
two additional peaks at 2
¼32.571 and 48.181 for CuInS2 (2 0 0),
y¼27.811 as shown in Fig. 1(c). By
y
In2S3 (4 4 0) reflections are clearly observed and the intensity for each
peak also increases, respectively. These results agree with the
literature [4,8,25] and for JCPDS no. [27-0159, 65-0459, 65-7111]
(see Fig. 1(d) and (e)). (1 1 2) and (2 0 0) peaks of CuInS2 and (4 4 0)
peak of In2S3 completely disappeared after annealing at 500 1C and
instead of these, (0 2 5), (1 1 0) peaks of CuS appeared. It is shown
that multilayer structure film converts CuInS2/In2S3 to CuS film due
to the high annealing temperature. This result can be interpreted as
follows: as the CuInS2/In2S3 thin film annealed at 500 1C, because the
vapor pressure of indium is lower than that of copper, indium is
evaporated from the substrate and the excessive copper occurs in the
CuInS2/In2S3 film. Thus, as shown in Fig. 1(f), the structure is con-
verted from CuInS2/In2S3 to CuS. This result is supported by the
higher mobility of copper ions and CuS segregation [26,27].
D ¼ K
l
=b
cos
y
ð4Þ
where D is the crystallite size,
l
is the X-ray wavelength used,
b
is
the angular line width of half maximum intensity,
y
is Bragg’s
Table 2
Annealing temperature and optical band gap values for annealed CuInS2/In2S3
thin films.
Annealing temperature (1C)
Band gap energy (eV)
200
300
400
500
2.48
2.49
2.51
2.69
All the results indicate that the crystallinity of these thin films
improved with increase in annealing temperature. The lattice
parameters of the films are given in Table 1 for CuInS2, In2S3 and
3.0x1010
3.0x1010
5.0
5.0
Annealed at 200°C
Eg = 2.48 eV
Annealed at 300°C
Eg = 2.49 eV
4.5
4.5
4.0
3.5
3.0
2.5
2.0
4.0
2.5x1010
2.0x1010
1.5x1010
1.0x1010
5.0x109
2.5x1010
3.5
3.0
2.0x1010
2.5
2.0
1.5x1010
1.0x1010
5.0x109
500 550 600 650 700 750 800 850 900
500 550 600 650 700 750 800 850 900
Wavelength (nm)
Wavelength (nm)
1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6
1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6
Energy (eV)
Energy (eV)
3.0x1010
2.5x1010
2.0x1010
1.5x1010
1.0x1010
5.0x109
3.0x1010
2.5x1010
2.0x1010
1.5x1010
1.0x1010
5.0x109
5.0
5.0
Annealed at 500°C
Eg = 2.69 eV
4.5
4.0
3.5
3.0
2.5
2.0
1.5
Annealed at 400°C
Eg = 2.51 eV
4.5
4.0
3.5
3.0
2.5
2.0
1.5
500 550 600 650 700 750 800 850 900
450 500 550 600 650 700 750 800 850 900
Wavelength (nm)
Wavelength (nm)
1.21.31.41.51.61.71.81.92.02.12.22.32.42.52.62.72.8
1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0
Energy (eV)
Energy (eV)
Fig. 3. Variation of absorbance with wavelength and graphs of a2 versus energy for thin films annealed at 200, 300 400 and 500 1C.

M. Kundakc-ı / Physica B 406 (2011) 2953–2961
2957
2
diffraction angle and K is a constant. The average crystallite size is
These plots [(
a)
versus (_
o
)] have been given in Fig. 3 and
calculated by resolving the greatest peak intensity. As seen in
Fig. 1(f), the (1 1 0) peak of CuS is very strong at the annealing
temperature of 500 1C. As can be seen in Fig. 2, the grain size
increases with increase in annealing temperature thus, crystalliza-
tion of films improves; this result agrees with the XRD pattern. The
grain size increases from 25.32 to 52.48 nm with the increase in
annealing temperature.
the band-gap energies of thin films were determined by the
extrapolation of the linear regions on the energy axis. Absorp-
tion edge is seen to be shifted to shorter wavelengths for
annealed films as shown in Fig. 3, which is a result of the
conversion from CuInS2 to CuS. As seen in Fig. 3, the band gap
has been found to be 2.48 eV for the thin film annealed at
200 1C and a correlation has been found between annealing and
band-gap such that increase in annealing temperature results
in an increase in the band-gap up to 2.69 eV, which is the band-
gap energy of CuS film (see Table 2). Both absorption and XRD
findings showed that the annealing at 500 1C of the grown
multilayer film structure converts the structure to CuS film. The
band gap energy values for 200, 300 and 400 1C annealing
temperatures belong to CuInS2 whereas, annealing at 500 1C
lead to obtain the band gap energy of CuS. Because the band
gap energy value of In2S3 thin film (2.9 eV, [28–30]) is greater
than that of CuInS2, the incident light is absorbed by the CuInS2
film. Consequently, the band gap value of CuInS2 can be found
via the optical absorption method. It is mentioned previously
that, because the vapor pressure of indium is lower than that of
3.2. Optical studies
The band gap energy of the films is calculated before and
after each annealing experiment with the help of absorption
spectra. First absorption data are converted into the absorption
coefficient as reviewed in our earlier reports [24]. The band-gap
2
calculation was done via the (
absorption coefficient and _
a)
versus (_
o
) plot, where
a
is the
o
is the photon energy. The absorp-
is proportional to:
tion coefficient
a
n
Instead of
að_oÞ ¼ Bð_o
ꢂEgÞ
ð5Þ
where B is a constant and n is an index (n¼1,2,3,y).
0.0034
0.0044
Annealed at 300°C
Annealed at 200°C
V = 5 volt
V = 5 volt
0.0042
0.0040
0.0038
0.0036
0.0034
0.0032
0.0030
0.0028
0.0026
0.0024
0.0032
0.0030
0.0028
0.0026
0.0024
0.0022
-5
0
5
10 15 20 25 30 35 40 45 50 55
0
5
10 15 20 25 30 35 40 45 50
Intensity (mW/cm2)
Intensity (mW/cm2)
60
58
56
54
52
50
48
46
44
42
Annealed at 400°C
V = 5 volt
Annealed at 500°C
V = 5 volt
0.10
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0
5
10 15 20 25 30 35 40 45 50
0
5
10 15 20 25 30 35 40 45 50
Intensity (mW/cm2)
Intensity (mW/cm2)
Fig. 4. Photocurrent versus light intensity for annealed CuInS2/In2S3 films.

2958
M. Kundakc-ı / Physica B 406 (2011) 2953–2961
copper, copper stays inside the structure, while indium evapo-
rates as a result of annealing process in the film that leads to an
increase in the band gap energy value. These values are greater
than the reported values of 1.5 eV for single CuInS2 crystals.
This can be interpreted either by poor crystallinity or by
deviations from stoichiometry that give rise to defect states,
which increase the band gap energy. As seen in XRD measure-
ments (Fig. 1), the structure of the films is converted from
CuInS2/In2S3 to CuS when the film is annealed at 500 1C.
Consequently, energy value of band gap (2.69 eV) is in good
agreement with the CuS thin film prepared by chemical bath
deposition (CBD) and SILAR [31–33].
5
4
Illumination (mW/cm2)
dark
15
30
50
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
The increase in Photocurrent
dark
3.3. Electrical properties
3.3.1. Photoconductive properties of CuInS2/In2S3 thin films
Various crystallinity imperfections in the film, such as vacan-
cies, dislocations and grain boundaries act as trapping or recom-
bination centers of the carriers and play an important role in
photoconduction. These traps act as localized positive potential
centers for electrons and negative potential centers for holes.
200 240 280 320 360 400 440 480 520
Annealing Temperature (°C)
Fig. 6. ln Photocurrent versus annealing temperature for annealed CuInS2/In2S3 films.
0.030
0.035
illumination (mW/cm2)
illumination (mW/cm2)
Dark
Dark
0.030
15
15
0.025
30
30
50
50
0.025
0.020
0.015
0.010
0.005
0.000
0.020
0.015
0.010
0.005
0.000
Annealed at 200°C
Annealed at 300°C
0
2
4
6
8
10 12 14 16 18 20 22
0
2
4
6
8
10 12 14 16 18 20 22
Voltage (V)
Voltage (V)
illumination (mW/cm2)
illumination (mW/cm2)
65
60
55
50
45
40
35
30
25
20
15
10
Dark
Dark
0.4
0.3
0.2
0.1
0.0
15
30
50
15
30
50
Annealed at 400°C
Annealed at 500°C
0
2
4
6
8
10 12 14 16 18 20
1
2
3
4
5
6
7
Voltage (V)
Voltage (V)
Fig. 5. Photocurrent versus voltage for annealed CuInS2/In2S3 films.

M. Kundakc-ı / Physica B 406 (2011) 2953–2961
2959
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
3.5
Light Intensity (mW/cm2)
Annealed Samples
200°C
15
30
50
3.0
2.5
2.0
1.5
1.0
0.5
0.0
300°C
400°C
500°C
V=5 Volt
V= 5 Volt
10
20
30
40
50
0
200
250
300
350
400
450
500
Ligth Intensity (mW/cm2)
Annealing Temperature (°C)
Fig. 7. (a) Photosensitivity versus light intensity and (b) Photosensitivity versus annealing temperature for annealed CuInS2/In2S3 films.
7.80
7.75
7.70
7.65
7.60
7.55
7.50
7.45
7.40
5.5
Annealed at 200°C
5.4
5.3
5.2
5.1
5.0
4.9
4.8
4.7
4.6
4.5
4.4
4.3
4.2
4.1
Annealed at 300°C
Ea = 0.023 eV
Ea = 0.052 eV
Ea = 0.026 eV
Ea = 0.253 eV
2.2x10-3 2.4x10-3 2.6x10-3 2.8x10-3 3.0x10-3 3.2x10-3 3.4x10-3
2.2x10-3 2.4x10-3 2.6x10-3 2.8x10-3 3.0x10-3 3.2x10-3 3.4x10-3
1/T (K)
1/T (K)
4.78
4.76
4.74
4.72
4.70
4.68
4.66
4.64
4.62
4.60
4.52
4.50
4.48
4.46
4.44
4.42
4.40
4.38
4.36
4.34
Annealed at 400°C
Ea = 0.008 eV
Annealed at 500°C
Ea = 0.009eV
E =0.022 eV
a
E =0.026 eV
a
2.2x10-3 2.4x10-3 2.6x10-3 2.8x10-3 3.0x10-3 3.2x10-3 3.4x10-3
2.2x10-3 2.4x10-3 2.6x10-3 2.8x10-3 3.0x10-3 3.2x10-3 3.4x10-3
1/T (K)
1/T (K)
Fig. 8. ln
r versus 1/T (K) for annealed CuInS2/In2S3 films.

2960
M. Kundakc-ı / Physica B 406 (2011) 2953–2961
Therefore, some localized discrete energy levels are formed in the
band gap, in the vicinity of the conduction and valence bands.
Fig. 4 shows the variation of photocurrent with light intensity in
CuInS2/In2S3 film for different annealing temperatures. The varia-
tion of photocurrent with applied voltage in CuInS2/In2S3 films is
shown in Fig. 5. It is clear that the photocurrent increases with
increase in voltage. The photocurrent is found to increase with
higher annealing temperature and light intensity. As annealing
temperature of the film increases, the crystallinity grain size
increases and this helps in the improvement of photocurrent.
The increase in photocurrent is attributed to an increase in the
majority carrier concentration and/or an increase in impurity
centers acting as traps for minority carriers as a result of
annealing. Especially at 400 1C annealing temperature, this
increase in photocurrent compared with other samples is much
more. This result is supported by Fig. 6. In this figure, logarithmic
photocurrent versus annealing temperature is shown, in order to
show the photocurrent of all samples in the same graph.
temperature for the CuInS2/In2S3 thin films is 400 1C. These
results agree with the literature [35,36].
3.3.2. Electrical resistivity
The electrical resistivity (r) of the films deposited with
different annealing temperatures has been measured in the
temperature range 300–470 K by the two dc probe method.
Plots of ln(r) versus 1/T for different annealing temperatures
are shown in Fig. 8. From the slopes of these plots, the values of
activation energies for low and high temperature linear regions
are calculated. It is observed that the resistivity changes non-
linearly with the increase in temperature, which is a semi-
conducting behavior. Formation of the film with discontinuous
clusters and ionizing impurity levels are the two reasons of this
non-linear behavior. The electrical resistivity values, which are
calculated at 300 K are given in Table 3. There is a huge decrease
in the resistivity values as the annealing temperature increases
from 200 to 500 1C (Table 3 and Fig. 9). The predicted reasons for
high resistivity are: nanocrystalline nature, crystallite boundary
discontinuities and presence of defect states. The decrease in
resistivity may be attributed to the presence of high conductivity
CuS phase segregation in the grain boundaries (from XRD results)
and high mobility of copper ions as mentioned above [26,27,37].
Photosensitivity is the ratio of the increase in conductivity of
the material in the presence of light to the conductivity in
darkness and is given by the following relation [34]:
S ¼ ðIphotoꢂIdarkÞ=Idark
ð6Þ
where Iphoto and Idark are the currents, measured under illumina-
tion and in the dark, respectively. Fig. 7(a) and (b) shows the plot
of photosensitivity versus light intensity and photosensitivity
versus annealing temperature, respectively. As can be seen in
Fig. 7, the value of photosensitivity has a maximum at the 400 1C
annealing temperature. As a result of annealing at 400 1C, some
transitions which create additional free carriers effectively
increase the free life time, which leads to an increase in photo-
sensitivity of the material. This result is supported by Figs. 5 and
6. As a result, it can be concluded that the optimum annealing
4. Conclusion
CuInS2/In2S3 thin films were prepared on glass substrate by
Successive Ionic Layer Adsorption and Reaction method and
annealed at 100, 200, 300, 400 and 500 1C for 30 min. It is found
that the annealing temperature is crucial for structural, optical
and photoelectrical properties. As the annealing temperature
increases from 200 to 400 1C, the CuInS2/In2S3 films show a wide
range of resistivity decrease from 2322.26 to 91.06
O cm. Photo-
sensitivity has maximum value and that of resistivity hass
minimum value at the 400 1C annealing temperature. Also, from
the XRD measurements, the best quality crystallinity is shown at
400 1C annealing temperature for CuInS2/In2S3 films. When the
annealing temperature is 500 1C, the structure of film is converted
from CuInS2/In2S3 to CuS. After all these results, it can be
concluded that the annealing temperature has an important role
in CuInS2/In2S3 multilayer films’ optical, structural and electrical
properties. Furthermore, 400 1C is found to be the optimum
annealing temperature for these properties.
Table 3
Resistivity values of annealed CuInS2/In2S3 thin films for different annealing
temperatures.
Annealing temperature (1C)
Resistivity (X cm)
200
300
400
500
2322.26
214.69
91.06
118.10
2500
2250
2000
1750
1500
1250
1000
750
Acknowledgment
This work was supported by the Ataturk University Research
Fund Project, Project Numbers 2010/286 and 2010/287.
References
[1] J. Klaer, J. Bruns, R. Henninger, K. Siemer, R. Klenk, K. Ellmer, D. Braunig, Sci.
Technol. 13 (1998) 1456.
[2] J.A. Hollingsworth, K.K. Banger, M.H.-C. Jin, J.D. Harris, J.E. Cowen,
E.W. Bohannan, J.A. Switzer, W.E. Buhro, A.F. Hepp, Thin Solid Films 431–
432 (2003) 63.
[3] H.J. Muffler, Ch. -H. Fischer, K. Diesner, M.C. Lux-Steiner, Sol. Energy Mater.
Sol. Cells 67 (2001) 121.
500
ꢀ
[4] M.C. Zouaghi, T. Ben Nasrallah, S. Marsillac, J.C. Bernede, S. Belgacem, Thin
Solid Films 382 (2001) 39.
[5] S. Kuranouchi, T. Nakazawa, Sol. Energy Mater. Sol. Cells 50 (1998) 31.
[6] R. Scheer, I. Luck, M. Kanis, M. Matsui, T. Watanabe, T. Yamamoto, Thin Solid
Films 392 (2001) 1.
[7] H.M. Pathan, C.D. Lokhande, Appl. Surf. Sci. 239 (2004) 11.
[8] P. Guha, D. Das, A.B. Maity, D. Ganguli, S. Chaudhuri, Sol. Energy Mater. Sol.
Cells 80 (2003) 115.
250
0
200
250
300
350
400
450
500
Annealing Temperature (°C)
[9] R. Scheer, T. Walter, H.W. Schock, M.L. Fearheiley, H.J. Lewerenz, Appl. Phys.
Lett. 63 (1993) 3294.
Fig. 9. Variation of resistivity as a function of annealing temperature.

M. Kundakc-ı / Physica B 406 (2011) 2953–2961
2961
[10] Y. Ogawa, A. Jager-Waldau, Y. Hashimoto, K. Ito, Jpn. J. Appl. Phys. 33 (1994)
[23] Y.F. Nicolau, Appl. Surf. Sci. 22/23 (1985) 1061.
L1775.
[24] M. Kundakci, A. Ates, A. Astam, M. Yildirim, Physica E 40 (2008) 600.
[11] T. Watanabe, M. Matsui, J. Appl. Phys. 38 (1999) L1379.
[12] Y. Onuma, K. Takeuchi, S. Ichikawa, M. Harada, H. Tanaka, A. Koizumi,
Y. Miyajima, Sol. Energy Mater. Sol. Cells 69 (2001) 261.
[13] K. Siemer, J. Klaer, I. Luck, J. Bruns, R. Klenk, D. Braunig, Sol. Energy Mater. Sol.
Cells 67 (2001) 159.
[25] M. Kundakci, Ph.D. Thesis, Ataturk University Grad. School of Nat. and Appl.
Sci, Erzurum, Turkey 2007, unpublished.
[26] M. Krunks, V. Mikli, O. Bijakina, H. Rebane, A. Mere, T. Varema, E. Mellikov,
Thin Solid Films 361–362 (2004) 61.
[27] M. Krunks, V. Mikli, O. Bijakina, E. Mellikov, Appl. Surf. Sci. 142 (1999) 356.
[28] N. Barreau, S. Marsiilac, J. Bernede, T. Nasrallah, S. Belgacem, Phys. Status
Solidi (a) 184 (2001) 179.
[14] J. Klaery, J. Bruns, R. Henninger, K. Siemer, R. Klenk, K. Ellmerand, D. Braunig,
Semicond. Sci. Technol. 13 (1998) 1456.
[15] Rahana Yoosuf, M.K. Jayaraj, Sol. Energy Mater. Sol. Cells 89 (2005) 85.
[16] D. Hariskos, M. Ruckh, Ulfert Ru¨hle, T. WalterHan, W. Schock, J. Hedstro¨m,
L. Stoltnovel, Sol. Energy Mater. Sol. Cells 41/42 (1996) 345.
[17] D. Braunger, D. Hariskos, T. Walter, H.W. Schock, Sol. Energy Mater. Sol. Cells
40 (1996) 97.
[18] A. Ennaoui, M. Weber, R. Scheer, H.J. Lewerenz, Sol. Energy Mater. Sol. Cells
54 (1998) 277.
[19] M. Chaparro, C. Maffiotte, M.T. Gutierrez, J. Herrero, J. Klaer, K. Siemer,
D. Braunig, Thin Solid Films 387 (2001) 104.
[20] A.M. Chaparro, M.T. Gutierrez, J. Herrero, J. Klaer, M.J. Romero, M.M.
Al-Jassim, Prog. Photovolt. Res. Appl. 10 (2002) 465.
[21] G. Gordillo, C. Calderon, Sol. Energy Mater. Sol. Cells 77 (2003) 163.
[22] N. Naghavi, S. Spiering, M. Powalla, B. Cavana, D. Lincot, Prog. Photovolt. Res.
Appl. 11 (2003) 437.
[29] J. Theresa, S. Bini, Y. Kashiwaba, T. Abe, Y. Yasuhiro, C.K. Sudha,
K. Vijayakumar, Semicond. Sci. Technol. 18 (2003) 491.
[30] H.M. Pahtan, C.D. Lokhande, S.S. Kulkarni, D.P. Amalnerkar, T. Seth, H.S. Han
Sung, Mater. Res. Bull. 40 (2005) 1018.
[31] K.M. Gadave, C.D. Lokhande, Thin Solid Films 229 (1993) 1.
[32] S.D. Sartale, C.D. Lokhande, Mater. Chem. Phys. 65 (2000) 63.
[33] I. Puspitasari, T.P. Gujar, K.D. Jung, O.S. Joo, Mater. Sci. Eng. B 140 (2007) 199.
[34] P.J. George, A. Sanchez-Juarez, P.K. Nair, Semicond. Sci. Technol. 11 (1996)
1090.
[35] R. Scheer, R. Klenk, J. Klaer, I. Luck, Sol. Energy 77 (2004) 777.
[36] T. Theresa John, M. Mathew, C. Sudha Kartha, K.P. Vijayakumar, T. Abe,
Y. Kashiwaba, Sol. Energy Mater. Sol. Cells 89 (2005) 27.
[37] H.M. Pathan, C.D. Lokhande, Appl. Surf. Sci. 239 (2004) 11.