The structural and electronic properties of amorphous silicon based alloy materials

The structure and electronic properties of hydrogenated amorphous silicon and its alloys are described, emphasizing localized states in the gap and interface states. The FSR and photoconductivity studies of prolonged illumination have led to a new model for the Staebler-Wronski effect, in which extra dangling bonds are created as a consequence of recombination. There is new evidence that the effect does not require the presence of impurities. DDTS and optical studies of gap states confirm that the dangling bond states are near mid-gap. Detailed information is presented concerning their role as recombination centers, through luminescence, ESR, and photoconductivity experiments. New localized states associated with phosphorus impurities were observed by ESR, although their structural identity is not yet known. Time-of-flight measurements of compensated a-Si:H show that although the dangling bond density is low, compensation introduces other states near the band edges that could be boron-phosphorus complexes. Inverse photoemission has measured the conduction band density of states, identifying Si-H artibonding states and the approximate location of the mobility edge.