FREQUENCY SCALING OF THE LOW-TEMPERATURE PHOTOCONDUCTIVITY OF AMORPHOUS-SILICON

The photoconductivity of intrinsic hydrogenated amorphous silicon has been measured between 12 K and 50 K at DC and at audio frequencies. The data for different intensities of illumination normalized to the appropriate DC photoconductivity sigma-1(0) follow a universal function of the reduced frequency omega/sigma-1(0). This scaling behaviour suggests strongly that the underlying recombination mechanism involves hopping in band tails. Compensated samples containing significant potential fluctuations have an almost identical response, implying that carriers trapped in wells in the bands do not contribute significantly to the loss. The data are discussed in the light of recent theoretical models.