Modelling of the structure of CdS thin films

The structure of CdS thin films produced by chemical bath deposition for wi ndow layers for photovoltaic devices has been investigated using the techni ques of standard theta-2 theta X-ray diffraction (XRD) and glancing angle X RD (GAXRD). The relative peal, intensities observed in the diffraction patt erns were consistent neither with a cubic nor a hexagonal microstructure. B y employing both diffraction geometries on the same sample it was establish ed that the Cd layers were un-textured. thus a structure different from eit her the cubic or hexagonal modifications was inferred. In order to elucidat e the crystalline structure of the material a Rietveld analysis program was employed, together with a special program written to generate appropriate input parameter files. It was found that a good match between experimental and simulated patterns could be obtained by postulating a polytype CdS stru cture, consisting of nearly random stocking sequences of the hexagonal plan es that form the basis for both the cubic (zinc-blende) and hexagonal (wurz ite) modifications. Thr GAXRD results indicate that little structural chang e occurs in the polytype CdS upon annealing in air, despite a pronounced co lour change. The structural difference between films deposited under differ ent conditions is much more pronounced than that between as-deposited and a nnealed material. The results are discussed with reference to investigation s by other authors of CdS thin films and of CdS nanoparticles using thr tec hniques of transmission electron microscopy and/or X-ray or electron diffra ction. (C) 2000 Published by Elsevier science S.A. All rights reserved.