Role of Substrate Temperatures on Structural, Optical, Wetting and Electrical Transport Properties of CdS Thin Films

P. D. More

Materials Research Laboratory, Department of Physics, Ahmednagar College, Ahmednagar, India.

DOI: 10.4236/jsemat.2013.31006                

Abstract

Cadmium sulphide thin films were deposited on the glass substrate via simple spray pyrolysis technique. The substrate temperatures (T_s) have been varied from 250℃ to 350℃ and concentration of precursor’s solution of cadmium chloride and thiourea was optimized. The X-ray patterns and morphological studies of CdS thin films indicated that films are crystalline in nature with hexagonal crystal structure. The grain size calculated and found to be 250.12 to 349.61 nm. The optical spectra exhibited high transmittance and band gap varied from 2.41 eV to 2.39 eV. The angle of contact measured and found to be hydrophilicity behaviour. The electrical conductivity and thermoelectric power have been measured with two probe method. It was found that CdS thin films were semiconducting in nature with n-type.

Keywords

CdS Thin Film; Spray Pyrolysis; Band Gap; Contact Angle

1. Introduction

The use of semiconducting materials in the form of thin films now a day’s occupy prominent place in the basic as well as applied research. It is a technologically useful material due to wide band gap of 2.42 eV, as many devices such as electronic devices including light emitting diodes, single electron transistors and field effect transistor [1] sensors [2] window materials [3]. CdS solar cell has several years been considered to be a promising alternative to the more widely used silicon devices [4]. The efficiency and performance of the devices depends on the optical and electrical properties of the thin films. So that attempt tried to understand the role of substrate temperatures on structural, optical, wetting and electrical transport properties of CdS thin films.

Thin film of CdS has been prepared by several methods including Vacuum [5] sputtering [6] spray pyrolysis [7,8] chemical bath deposition [9]. The interest to nonvacuum methods for thin films deposition has increased. The solution based processes have several advantages viz: simplicity of process, precise composition, applicability to substrates of any size. These are important for practical applications. The SPD meets practically all the requirements to the methods for the films deposition on large substrate [10].

2. Methodology

Cadmium sulphide thin films were deposited via spray pyrolysis technique using aqueous solution of cadmium chloride (CdCl₂ of 0.1 M) and thiourea (NH₂CSNH₂ of 0.2 M) at 250˚C, 300˚C and 350˚C substrate temperatures. The substrate was cleaned by ultrasonic cleaner. The samples were deposited by spraying 30 ml prepared solution at the rate of 5 ml/min using air as a carrier gas. The nozzle to substrate distance was kept around 22 cm.

The structural properties of CdS studied by X-ray diffraction (XRD) using filtered CuKα radiation (λ = 1.5406 Å). The surface morphologies of the CdS thin films carried out by scanning electron microscope operating at 25 KV. The optical studies carried in the range of 300 - 950 nm wavelengths. Contact angle of CdS were measured using standard goniometer (Ramehart Instrument Co., USA) equipped with CCD camera.

3. Results and Discussion

3.1. X-Ray Diffraction Studies

X-ray diffraction patterns of CdS films deposited at 250˚C, 300˚C and 350˚C substrate temperatures as shown in Figure 1. It is observed that XRD pattern showed preferential orientations along (100), (002) and (101) additionally (110), (103) and (201) directions. All the diffraction peaks can be indexed to a hexagonal structured. No obvious characteristic diffraction peaks from other impurities can be detected. From XRD studies it is clear that the intensity of peaks is function of substrate temperature and suggests that as deposited CdS films are crystalline

Figure 1. X-ray diffraction patterns of CdS thin films as a function of substrate temperatures.

in nature which is similar to reported in the literature [7,8].

Figure 2 shows the variation in intensity. The lattice parameters were calculated from the XRD data and are found to be close agreement with the JCPD data [11]. The grain size were calculated at q = 27.55˚ by using Scherer’s relation and listed in Table 1.

Conflicts of Interest

The authors declare no conflicts of interest.

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