Structural, electrical and optical properties of In-doped CdS thin films prepared by vacuum coevaporation

Abstract In-doped CdS films of 1 gmm thickness for a window layer of solar cells have been prepared by vacuum coevaporation of CdS and In on glass substrates at 150 °C. The In concentration in CdS films was varied from 1018 to 1021 cm−3. Structural, electrical and optical properties of CdS films have been investigated by X-ray diffraction, scanning electron microscopy, electrical resistivity measurement, the Hall effect and optical transmittance spectra. As the In concentration increased the preferred orientation of the films change from the (002) plane to the (110) plane. Also, the grain size became smaller and the grain shape changed. The electrical conductivity, carrier concentration and Hall mobility increased with increasing In concentration and then decreased with further increase in In concentration. CdS films became degenerate semiconductors as electron concentration exceeded 2 × 1018cm−3 and the optical band gap increased with increasing electron concentration due to the increase of the Fermi level in the conduction band. The optimum In concentration turned out to be 3 × 1020cm−3, which showed the lowest resistivity of 5 × 10−3ωcm and the largest optical band gap of 2.6 eV.