خصوصیات نوری فیلم های نازک تلورید کادمیوم تبخیر شده به روش حرارتی
Abstract
1. Introduction
2. Experimental
3. Results and discussion
4. Conclusions
Acknowledgements
References
Abstract
Polycrystalline CdTe films have been deposited onto glass substrates at 373 K by vacuum evaporation technique. The transmittance and reflectance have been measured at normal and near normal incidence, respectively, in the spectral range 200–2500 nm. The dependence of absorption coefficient, α on the photon energy have been determined. Analysis of the result showed that for CdTe films of different thicknesses, direct transition occurs with band gap energies in the range 1.45–1.52 eV. Refractive indices and extinction coefficients have been evaluated in the above spectral range. The XRD analysis confirmed that CdTe films are polycrystalline having hexagonal structure. The lattice parameters of thin films are almost matching with the JCPDS 82-0474 data for cadmium telluride. © 2002 Elsevier Science B.V. All rights reserved.
Introduction
Cadmium telluride is considered at present one of the most promising materials, for device applications. It has high absorption coefficient in the visible range of the solar spectrum and its band gap is close to the optimum value for efficient solar energy conversion [1,2]. The material can be prepared in n-type and p-type forms so that solar cells can be formed in both homojunction and heterojunction configurations. A survey of the literature shows that different techniques of deposition have been developed to obtain device grade CdTe thin films, among which electrodeposition [3], rf sputtering [4], closed vapor transport [5], spray pyrolysis [6], screen printing [7], and vacuum evaporation [8,9] are worth mentioning. All these techniques have their own merits and demerits in producing high quality CdTe films. Recently several workers have studied structural characteristic and optical properties depending on the deposition conditions [10–17]. Most of these investigations did not deal with each deposition condition, separately and some contradictions appeared in the results. Therefore in this work systematic investigation of the effect of the preparation conditions on the optical properties and structural characteristic has been carried out. An interpretation of the determined optical constant variations in correlation with the corresponding structural parameters is presented.