Elsevier

Optik

Volume 123, Issue 12, June 2012, Pages 1098-1102
Optik

The effect of annealing temperature on structural and optical properties of undoped and Cu doped CdS thin films

https://doi.org/10.1016/j.ijleo.2011.07.038Get rights and content

Abstract

Cadmium sulphide (CdS) thin films were prepared chemical bath deposition technique. The films were doped with copper using the direct method consisting in the addition of a copper salt in the deposition bath of CdS. The doped films were annealed in air, at 250, 300 and 350 °C, for 1 h. The deposition films were characterized with X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis by X-rays (EDAX) and optical properties of CdS thin films before and after Cu doping. XRD analysis shows that the films are polycrystalline in nature with cubic crystalline structure. The various parameters such as crystallite size, micro strain and dislocation density were evaluated. SEM study shows that the total substrate surface is well covered by uniformly distributed spherical shaped grains. Optical transmittance study shows the presence of direct transition with band gap energy decrease 2.5–2.2 eV.

Introduction

CdS films are often grown by the chemical bath deposition (CBD) technique, and have shown good properties for device fabrication. The chemical bath deposition of CdS films on glass substrates from aqueous solution is a low-cost process and it is well suited for the manufacture of film solar cells. CdS-CBD films are commonly used as a window or buffer layer material for solar cells of the type CdS/CdTe and CdS/CIGS [1], [2], [3], [4]. Also, there have been studies on Cu doped CdS to obtain p-type Cu:CdS. Generally, they have obtained p-type of these samples by diffusion of Cu. They have achieved an efficiency of 6–7% by a Cu: CdS/CdS homostructure for photovoltaic applications [5], [6]. The efficiency of solar cells is found to be improved with an increase in the conductivity of the Cu:CdS films.

The deposition of CdS films has been explored by different techniques such as thermal evaporation [7], [8], molecular beam epitaxy [9] and spray pyrolysis [10], anodic oxidation [11], cathodic reduction [12] and chemical bath deposition [13]. Development of the chemical bath deposition is widely used because it is a simple and economic and viable technique, which produces films of good quality for device application. This technique has already used for preparation of various semiconducting compound and alloy thin films.

In the present work, an attempt is made to prepare CdS and Cu:CdS thin films by simple and low cost chemical bath deposition technique. The films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis and optical properties and the results are discussed.

Section snippets

Experimental technique

The undoped CdS and Cu doped CdS thin films were obtained by the method of chemical bath deposition technique. Chemicals used for the deposition of CdS and Cu:CdS were analytical grade cadmium chloride, thiourea, and copper chloride, ammonium hydroxide, and de-ionized water.

The deposition of CdS thin films was performed on glass substrates, immersed in the composition of 0.2 M cadmium chloride (CdCl2·2H2O) was dissolved in 50 ml of de-ionized water and stirred for 10 min using magnetic stirrer. NH4

XRD analysis

XRD patterns of the chemical bath deposited thin films prepared on glass substrates with bath composition 0.2 M CdCl2, 0.2 M SC(NH2)2 and 0.0005 M CuCl2 at bath temperature 80 ± 5 °C are shown in Fig. 1(a)–(d). The XRD patterns revealed that the deposited films are found to be cubic crystal structure is highest peak corresponds to the (1 1 1), (2 2 0), and (3 1 1) phase of undoped and Cu doped CdS. The different peaks in the diffractogram were indexed and the corresponding values of interplanar spacing “d

Conclusions

The CdS and Cu:CdS thin films are potential candidates used in various application like solar cells and hence they were taken for the present work. The CdS and Cu:CdS thin films were deposited glass substrates at bath temperature 80 ± 5 °C after annealed at different temperatures using an chemical bath deposition technique. X-ray diffraction analysis confirmed that the deposition CdS films are polycrystalline in nature with cubic structure and there is chance in the intensity, addition peaks and

Acknowledgements

The authors are grateful thanks to Sophisticated Test and Instrumentation Centre, Cochin, and Alagappa University, Karaikudi, for providing instrument facilities.

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