EFFECT OF PROCESSING CONDITIONS ON STRUCTURAL AND PHYSICAL-PROPERTIESOF CD-RICH THIN-FILMS OF CDTE

The physical properties of CdTe thin films formed by vacuum evaporatio n techniques onto glass substrates were studied as a function of the p rocessing conditions. The structure of CdTe films was examined using a n X-ray diffraction (XRD) technique. The films were polycrystalline an d cubic; they were grown with the (111) plane parallel to the substrat e. The lattice constant (a = 0.6470 nm) was found to be smaller than t hat for a stoichiometric samples. This indicates the presence of resid ual compression stresses or excess Cd in substitutional sites. The cry stallite size (10-72 nm) was found to increase with increasing substra te temperature (300-520 K). The films contained free Te which was vari ed with the substrate temperature. The variation of transmission withi n the wavelength range from 500 to 1000 nm was also investigated. It s howed a band edge at about 1.5 eV. The variations of conductivity and carrier concentration with temperature were investigated. The conducti vity data in the low-temperature region were analysed for variable ran ge-hopping conduction on the basis of Mott's model. The analysis of th e high-temperature conductivity data was based on Seto's model of ther mionic emission. On the other hand, it was found that excess Cd increa ses the conductivity. However, the density of trap states near the Fer mi level N(E(F)), was proportional to the Cd content.