Photocurrent spectral distribution in some crystalline and amorphous materials

The photocurrent spectral distribution in some crystalline and amorphous photoconductive materials has been theoretically investigated. The study is based on the bulk properties of the material and their effect on the bulk recombination lifetime of the photogenerated carriers. The lifetime is assumed to change with the density of the photogenerated free carriers. It is shown that the lifetime depends on the intensity as well as the wavelength of the incident light. The lifetime decreases with increase of light intensity and/or decrease of wavelength. The change of lifetime with wavelength can be used to explain the photocurrent peak which is observed at wavelengths corresponding to the band-gap energy. The explanation applies to crystalline and amorphous samples for which the photocurrent varies as the square root (or some other power smaller than unity) of the light intensity. Theoretical results are in good agreement with the experimental results of flux-grown crystalline TiO2, crystalline As2Se3, and some amorphous materials.