Photoinduced photocurrent decay in non-hydrogenated amorphous silicon nitride prepared by ion-beam-assisted reactive deposition

Abstract

Abstract Non-hydrogenated amorphous silicon nitride (a-SiNx) films have been prepared using ion-beam-assisted reactive deposition and N2 for the ion source gas. For a fixed ion beam voltage, a fixed Si deposition rate and a fixed substrate temperature, the N concentration in the film is determined by the ion beam current. At low N concentrations, the dark conductivities are dominated by hopping transport via the gap states. When the N content is increased, the gap state density is reduced and activated conductivities are observed. Room-temperature dark conductivities varying by ten orders of magnitude and optical bandgaps from 1.3 to 3.5 eV were obtained by changing the N concentration. Films with a ratio N N/N Si of N to Si content greater than 0.7 were photoconducting and this degraded slowly over time with exposure to a mercury light source. Since care was taken to eliminate H from these films and no H was detected in the films by infrared absorption, this would suggest that H may not be needed for the photoinduced degradation mechanism in a-SiNx. In addition, evidence is given that suggests sample polarization occurs and this could explain the photoconductivity fatigue observed.