On the constant photoconductivity method in amorphous semiconductors

The authors investigate the validity of the constant photoconductivity method for obtaining the sub-band-gap absorption coefficient, and hence the density of states, in amorphous semiconductors. They find that in hydrogenated amorphous silicon the sub-band-gap photoconductivity is dominated by transitions from the valence band tail to the conduction band, while the density of recombination centres remains constant in conditions of constant photocurrent, the photoconductivity depends on a capture cross section which may show energy (and thus wavelength) dependence. The behaviour of the photoconductivity under varying illumination intensity is also determined.