| Popis: |
The research described in this report covers the structure and electronic properties of hydrogenated amorphous silicon and its alloys, emphasizing localized states in the gap and interface states. ESR 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. DLTS 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 have been 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 antibonding states and the approximate location of the mobility edge. NMR experiments find that thin films of a-Si:H have an excess hydrogen concentration and a new relaxation mechanism observed above 200/sup 0/K with an unknown origin. A widemore » variety of a-Si:H interfaces have also been studied.« less |
