Photoconducting properties of cadmium sulphide-lithium thin films formed by the chemical bath deposition method

Abstract

The cadmium sulphide-lithium thin films used in this work were prepared by the chemical bath deposition technique. In this simple process uniform large-area films of semiconducting and photoconducting cadmium sulphide can be formed on rotating substrates. The photoconducting and optical properties of these films were studied. The photoconducting properties studied included the rise and decay of the photoconductivity, the spectral response of the photoconductivity and the variation of the time constants with the wavelength of excitation and with the intensity of excitation. The photoconductivity rise curve for the first excitation was analysed considering the role of photodesorption of oxygen to determine the oxygen trap level, which is 0.78 eV below the conduction band. Although it was analysed using an old method developed by R.H. Bube, the oxygen trap level obtained is in good agreement with that found from the decay curve. The variation of the time constants with the intensity of illumination is explained on the basis of quasi-Fermi levels and the pinning of the quasi-Fermi levels somewhere in the band gap. This pinning arises from the high density of the filled traps at quasi-Fermi levels.