The effect of H on a-SiNx prepared by ion-beam-assisted reaction deposition

Abstract

a-SiNx:H films have been prepared using ion-beam-assisted deposition and source gases of NH3, or N2 + NH3 gas mixtures. Some optical and electrical properties were compared with those of nonhydrogenated a-SiNx films, prepared using pure N2 as the ion source gas. H can significantly alter the a-SiNx:H film properties, but the effects are different, depending on the source gas used. a-SiNx:H films, prepared using NH3 ion beams exhibit activated conductivities, are photoconducting and display photoconductivity fatigue effects. For the same N concentrations, the decay of a-SiNx:H is faster than that of a-SiNx. This could be due to an indirect role for H, i.e., its effect on the recombination centre density. a-SiN0.82:H prepared with an NH3 + N2 gas mixture contains more N—H bonds than Si—H bonds, and this is opposite to that found in a-SiNx:H, made using an ammonia ion beam. Even though the N concentrations and the total H concentrations are kept fairly constant in this group of films, the electrical activation energies, optical gaps and conductivities are different. The results suggest that the Si—H bond is more important than the N—H bond in determining the film properties for Si-rich films. The photoconductivities for the group of films made with the gas mixture are lower than those observed for a-SiNx:H films prepared with NH3 alone. In addition, the mixing of NH3 with N2 for the ion source reduces both the optical gaps and the activation energies, and increases the dark conductivities of the films for the same N concentration, when a lower NH3/(NH3 + N2) gas ratio is used.