Density of states and mobility—lifetime product in hydrogenated amorphous silicon, from thermostimulated conductivity and photoconductivity measurements

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Abstract
By combining thermostimulated conductivity and photoconductivity measurements, the density of gap states g(E) as well as the product of the microscopic mobility μ and the recombination lifetime τ of various samples containing hydrogenated amorphous silicon (a-Si:H) have been determined. The results obtained on pure a-Si: H are compared with those of nitrogen-doped a-Si: H films and of multi-layer structures consisting of alternating layers of 570 Å thick a-Si: H and 30 Å thick a-SiNx: H. A large density of states in the latter material is attributed to interface states. The μτ products measured are several orders of magnitude larger than the product of drift mobility and deep trapping time obtained from time-of-flight and charge-collection experiments. The results suggest that in addition to dangling bonds there are other recombination centres.