Native defects in hexagonalβ-Si3N4studied using density functional theory calculations

Abstract

A comprehensive study of single native point defects in hexagonal silicon nitride ($\ensuremath{\beta}$-Si${}_{3}$${\mathrm{N}}_{4}$) has been carried out based on density functional calculations of formation energies. Both nitrogen- and silicon-rich native defect centers form donor and acceptor states in the band gap of $\ensuremath{\beta}$-Si${}_{3}$${\mathrm{N}}_{4}$, confirming their amphoteric behavior. Silicon dangling bonds resulting from structural nitrogen vacancies (${V}_{\mathrm{N}}$) are the most abundant native defects, in particular, in their acceptor state (${V}_{\mathrm{N}}^{\ensuremath{-}}$ and ${\mathrm{V}}_{\mathrm{N}}^{3\ensuremath{-}}$). Hydrogenation promotes the appearance of Si dangling bond defects in the neutral state consistent with the observation of paramagnetic centers in the gap of amorphous silicon nitrides by electron spin resonance. This explains the utility of silicon nitride as charge trapping layer in nonvolatile memories.