Abstract
A theoretical treatment is presented in which the small-signal, space-charge capacitance, C sc, in a-Si MIS structures is calculated for varying levels of illumination. Bulk recombination and a sufficient density of states at the insulator-semiconductor interface to pin the Fermi level and produce a significant surface band-bending are assumed. It is shown that the trapping state density as a function of energy in the mobility gap can be derived from measurement of C sc at different levels of illumination. The method is particularly applicable in cases where the surface-state density is large enough to preclude field-effect measurements.