A novel technique has been proposed for determining the density-of-state (DOS) distribution in the mobility gap of highly resistive amorphous semiconductors, using amorphous/crystalline heterojunction structures. This technique has been tested and applied on undoped a-Si:H and a-SiGe:H films, covering the optical gap (E0 ) range of 1.30 to 1.76 eV. For undoped a-Si:H with E0 =1.76 eV, the peak of the midgap DOS distribution has been locatedst 0.85 eV below the conduction band edge, EC , with a value of 5.6×1015 cm-3 eV-1 . For undoped a-SiGe:H (E0 =1.55 eV) the same has been obtained 0.71 eV below EC with a magnitude of 7.9×1016 cm-3 eV-1. Those midgap states have been found to be correlated with singly-occupied dangling bonds.
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Matsuura, H., Tanaka, K. The Density-of-State Distribution in Undoped a-Si:H and a-SiGe:H Determined by Heterojunctions with c-Si. MRS Online Proceedings Library 118, 647 (1988). https://doi.org/10.1557/PROC-118-647