Properties of chemically deposited CdS thin films converted to n-type by indium diffusion

Structural, optical and electrical properties of chemically deposited CdS thin films (300 nm thickness), converted to n-type by thermal diffusion of indium are presented. CdS thin films were deposited at 80 degrees C for 4 h from a chemical bath containing citratocadmium ions and thiourea. The diffusion of indium from a source of evaporated thin indium film (10-40 nm thickness) on the surface of CdS film was carried out by heating the sample in air at 250-350 degrees C for 1-4 h. X-ray diffraction spectra of the films indicate the formation of a surface layer of In2O3 during the heat treatment. X-ray photoelectron spectroscopy studies show that, with the oxide film acting as a diffusion barrier, indium diffuses into the CdS thin film leading to the conversion of the chemically deposited intrinsic photosensitive CdS thin film to n-type with conductivity up to 50 Ohm(-1) cm(-1). Optical transmittance spectra of the films indicate that the n-type CdS films formed in this way retain the basic features of the spectra of chemically deposited CdS thin films, notably an optical band gap > 2.5 eV.