D Kathirvel

N Suriyanarayanan

S Prabahar

S Srikanth

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International Journal of Physics (IJP), Volume 1, Issue 1, January- March 2012 
8 
 
 
 
 
 
ELECTRICAL PROPERTIES OF CHEMICAL BATH 
DEPOSITED CdS THIN FILMS 
D Kathirvel a*, N Suriyanarayanan b, S Prabahar c, S Srikanth c 
a* Department of Physics, Kalaignar Karunanidhi Institute of Technology,Coimbatore 
b Department of Physics, Government College of Technology, Coimbatore, India. 
c Department of Physics, Tamilnadu College of Engineering, Coimbatore, India. 
 
ABSTRACT 
 Thin films of CdS of different thickness have been prepared on glass substrates in 
various temperatures by Chemical bath deposition. Electrical resistivity measurements 
were carried out in four-probe vander pavu geometry at room temperature. Resistivity of 
CdS thin films is about 108Ωcm. Typical linear dark I-V characteristics of the CdS thin 
films and ohmic behavior is observed.   
Keywords: Electrical resistivity, Chemical bath deposition, CdS thin films, I-V 
characteristics. 
INTRODUCTION 
 Chemical bath deposition is a well known deposition process for Chalcogenides 
such as Cd, Zn, Co, Hg, Pb sulphides and selenides [1]. The Chemical Bath Deposition 
(CBD) method, being less expensive than other thin film deposition methods allows for 
the manufacture of relatively low cost devices especially light detectors, light energy 
conversion cells and thin films field effect transistor [2, 3]. CdS in an important 
semiconductor material with very narrow band gap (2.10 to 2.40eV). The CdS material 
INTERNATIONAL JOURNAL OF PHYSICS 
 
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Volume 1, Issue 1, January- March (2012), pp. 08-14 
© IAEME: www.iaeme.com/ijp.html 
 
 
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International Journal of Physics (IJP), Volume 1, Issue 1, January- March 2012 
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exhibits hexagonal structure with a preferred orientation along (002), (116,312) and 
(316,332) directions [4, 5]. In this paper we present the results of our studies on electrical 
studies of Chemical Bath Deposited CdS thin film. 
EXPERIMENT 
 A simple Chemical bath deposition (CBD) method was employed to deposit CdS 
thin films on to glass substrates using thiourea as sulfide ion source and cadmium 
sulphate as cadmium ion source in Ammonia bath. For the preparation of CdS thin films, 
110ml of water heated upto 700c and glass substrates was inserted and 0.0623M 
Cadmium sulphate was added with slow stirring of the precipitated solution. Ammonia 
solution (NH3) was then added. When adding ammonia solution, the temperature of 
precipitated solution was reduced. Then 0.3284M Thiourea was added slowly in the 
solution. After adding thiourea, the precipitated solution became a yellowish colour 
which indicates the production of Cadmium sulfide in the precipitated solution. Time 
taken for the growth of the Cadmium Sulfide on the glass substrates varied from 30 
minutes to 45 minutes. Substrate cleaning plays an important role in the deposition of 
thin films. Commercially available glass micro slides were submerged into the chromic 
acid for upto 2 to 3 hours. Then the glass substrates are washed with detergent and finally 
rinsed with acetone before use. The films with different thickness were obtained by 
varying the deposition time period. The thickness of the CdS thin films are measured by 
using gravimetric method [6, 7]. The thickness variation of successive film is in the range 
of 90 Å in CdSo4 combination. The nature of the electrical properties was examined by 
four-probe vander pavu geometry at room temperature. The arrangement consists of PID 
controlled oven (Model PID-2000, Scientific Equipment and services, Roorkee, India). 
The thickness dependent current-voltage behavior of Schottky devices was studied using Janis 
Liquid Nitrogen VPF Series Cryostat. Rotary pump was used to maintain desired vacuum 
inside the cryostat. 
 
 
International Journal of Physics (IJP), Volume 1, Issue 1, January- March 2012 
10 
 
RESULT AND DISCUSSION 
RESISTIVITY STUDIES 
In semiconductor industry the most generally used technique for the measurement 
of resistivity is the Four- Point Probe. Current is passed thought the outer two probes and 
the potential developed across the inner two probes. Further, it is after convenient to 
present the current to 2πS milliamperes or microamperes so that the resistivity in ohm-
centimeters will be numerically equal to the measured voltage in milli-or micro volts, 
respectively.  
 
Fig. 1. Fig.2. and Fig.3. show the variation of log ρ against reciprocal of 
temperature (1000/T) with different thickness of 560Å, 1180 Å & 1700 Å is measured 
using the d.c. four probe method in air.  
 
 
 
Fig. 1.  Resistivity Vs (1000/T) of CdS thin film at d = 560 Å 
International Journal of Physics (IJP), Volume 1, Issue 1, January- March 2012 
11 
 
 
Fig. 2.  Resistivity Vs (1000/T) of CdS thin film at d = 1180 Å 
 
Fig. 3.  Resistivity Vs (1000/T) of CdS thin film at d = 1700 Å 
From the resistivity plot, the variation of resistivity and activation energy at 
different thickness of CdS films are shown in Table 1.  
Table 1. Variation of resistivity and activation energy with different thickness  
Sl. No. Film thickness (Å) Resistivity (Ω cm) Activation energy (eV) 
1 560 Å 2.54 x 106 0.6403 
International Journal of Physics (IJP), Volume 1, Issue 1, January- March 2012 
12 
 
2 1180 Å 3.28 x 106 0.7498 
3 1700 Å 9.87 x 106 0.7874 
 
The resistivity of as deposited CdS thin film obtained by chemical bath 
deposition at room temperature is too high. Table 1. shows activation energies at 
different thickness of CdS film. Activation energies are in the range of 0.6345 eV to 
0.7095.  
I-V Characteristics of CdS thin films. 
The I-V characteristic without illumination (in dark), the forward current of the 
cell increases slowly with increasing voltage is shown in Fig. 4. over the CdS thin films 
of thickness 560 Å, 1180 Å and 1700 Å. 
The short circuit current ISC corresponds to the short circuit condition when the 
impedance is low and is calculated when the voltage equals 0.   
           I (at V=0) = ISC         ----------------  (1) 
From the Fig. 4, the heterojunction has rectification properties and the 
current increases with increasing thickness. Since the dark I - V plots are similar to 
the diode characteristics. ISC occurs at the beginning of the forward-bias sweep and is the 
maximum current value in the power quadrant.  
ISC = IMAX = Iℓ for forward-bias power quadrant. 
 
International Journal of Physics (IJP), Volume 1, Issue 1, January- March 2012 
13 
 
 
Fig. 4. I - V characteristics of CdS thin films in dark condition at different thickness 
by Chemical bath deposition. 
The open circuit voltage (VOC) occurs when there is no current passing through 
the cell.  
                                                      V (at I=0) = VOC            ----------------  (6.4)  
VOC is also the maximum voltage difference across the cell for a forward-bias 
sweep in the power quadrant. 
International Journal of Physics (IJP), Volume 1, Issue 1, January- March 2012 
14 
 
VOC= VMAX for forward-bias power quadrantP), Voltage at PMAX (VMP) 
The power produced by the cell in Watts can be easily calculated along the I-V 
sweep by the equation P=IV.   At the ISC and VOC points, the power will be zero and the 
maximum value for power will occur between the two.  The voltage and current at this 
maximum power point are denoted as VMP and IMP respectively. 
CONCLUSION 
CdS thin film has been deposited on a well cleaned glass substrate by chemical 
bath deposition technique. CdS shows n-type conductivity. Its resistivity is about 108 Ω 
cm. Carrier concentration is found to improve with Cd concentration in bath. 
Conductivity is found to improve with dosage. High resistivity is due to low-deposition 
temperature and as a consequence of that the film formed with a small grain size and 
thus contains many grain boundaries which in turn increase the resistivity. Through the 
hot point probe technique the film shows n-type conductivity. From the resistivity plot, 
the variation of resistivity and activation energy at different thickness of CdS films can be 
calculated. 
 CdS  exhibits characteristics compatible with window material for solar cells.  
REFERENCES 
[1] R.S. Mane, C.D. Lokhande, Thin solid films.65,1 (2000). 
[2] J.H. Schon, O.Schenker, B.Battogg, Thin solid films, 385,271 (2001). 
[3] A.Davis, K.Vaccaro, H.Dauplaise, W.Waters, J.Lorenzo, J.Electrochem.Soc.146, 
1046 (1999). 
[4] Sushilkumar, Zishan.H.Khan, M.A. Majeed Khan, M.Husain, Current Applied 
Physics.5, 561 (2001). 
[5] J.Dona, J.Herrero, J.Electrochem.Soc, 139, 2810 (1992). 
[6] H.Metin, R.Esen, Semicond.Sci.Technol, 18, 647 (2003). 
[7] I.Oladeji, L.Chow, J.Electrochem. Soc, 144, 2342 (1997).  
 
 
*Corresponding author: kathirvelde.5@gmail.com 


ELECTRICAL PROPERTIES OF CHEMICAL BATH DEPOSITED CdS THIN FILMS

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ELECTRICAL PROPERTIES OF CHEMICAL BATH DEPOSITED CdS THIN FILMS

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