Light-induced metastable changes in amorphous silicon nitride

Light-induced metastable increases in subgap absorption have been studied in semi-insulating amorphous silicon nitride as a function of illumination temperature between 100 and 300 K. These metastable absorption changes can be partially bleached by subgap light. The metastable increase in subgap absorption is related to neutralization of charged dangling-bond defects. Thermal relaxation of the metastable state is modelled by phonon-assisted hopping of carriers between neutral defects. We explain the persistent photoconductivity of amorphous silicon/silicon nitride multilayers with metastable hole trapping by defects in the nitride layers. We explore the origin of the charge state of dangling-bond defects in silicon nitride and conclude that the origin is more likely potential fluctuations than a negative effective correlation energy. The similarity of light-induced metastable changes in other materials suggests an origin that is common to semi-insulating amorphous alloys.