Dual impurity doping of buffer solution grown cadmium sulphide thin films: electrical and optical properties

Abstract

The effects of incorporation of aluminum and chlorine simultaneously into buffer solution grown cadmium sulphide thin films (i.e. dual impurity doping), on the electrical and optical properties of the films for various concentrations of aluminum and chlorine in the range 0.0002–0.01 wt % have been investigated. The results showed that the thicknesses (and optical absorption) of aluminum doped CdS films increased slightly as the aluminum concentration was increased, leading to decrease in optical transmittance and bandgap energy, and improvement of the dark electrical conductivity of the films. For aluminum concentrations of 0.01 wt % and above, the electrical conductivity of the doped CdS films was impaired. The dark electrical conductivity of aluminum-doped CdS films is at least ten times that of pure Cds film and at least one hundred times in the presence of chlorine. Generally, in the presence of chlorine, the electrical conductivity and the optical transmittance of the aluminum-doped CdS films were improved to some extent for aluminum concentrations ≤0.001 wt %. Optical bandgap varies from 2.45 eV for pure CdS film to 2.30–2.35 eV for doped films. The possible mechanisms for these observed effects are discussed. © 2000 Kluwer Academic Publishers