Evidence for the defect-pool model from induced recombination level shifts in undoped a-Si:H

The measured dependence of the mobility-lifetime products for electrons and holes, on the relative position of the dark Fermi level EF in undoped hydrogenated amorphous silicon, a-Si:H, is reported here. The corresponding measurements, which also included the EF dependencies of the light-intensity exponents and S, became feasible due to the use of a combination of metal-oxide-semiconductor and photocarrier grating configurations. We found that the experimental results of the S(EF) dependence are very helpful in determining which of the models proposed for the recombination-center distribution in the mobility gap of a-Si:H is the most appropriate one.