Studies on chemically deposited CdS 1 − xSe x mixed thin films

Abstract

A solution growth process is employed for the deposition of CdS 1 − x Se x thin film composites with 0 ≤ x≤ 1. Cadmium acetate, thiourea and sodium selenosulphate were used as the basic source materials. The samples were obtained at 55 °C in an alkaline medium and were characterised by optical and electrical characterisation techniques. The layer thickness is found to be decreased as x is varied from 0 to 1. The optical absorption studies showed a high coefficient of absorption ( α = 10 4 cm −1) with an allowed direct type of transition. The optical energy gap decreases continuously (typically from 2.42 eV to 1.74 eV) as x is increased from 0 to 1. For values of x between 0.5 and 0.8, two absorption edges have been observed; one at approximately 2.40 eV corresponding to the fundamental optical transitions in CdS and the other decreasing continuously, which corresponds to the fundamental transitions in CdS 1 − x Se x solid solution. The electrical conductivity is found to decrease up to x = 0.5 and to increase thereafter for further increase in x. The activation energy is more or less the same for all compositions and has no systematic dependence on the composition parameter x.