Electronic Structure of Defects in Amorphous Silicon Nitride

Abstract

ABSTRACTThe paper reviews the electronic properties of defects in amorphous silicon nitride (a-Si3N4) and the hydrogenated alloys a-SiNx:H. The main defects in a-Si3N4 are the Si and N dangling bonds (DBs). The Si DB forms a sp3 state near midgap, while the N DB forms a highly localized pπ level just above the valence band edge. The behaviour of the alloys changes near x ≈ 1.1, the percolation threshold of Si-Si bonds. In the Si-rich alloys, both band edges are Si-like, only Si DBs are seen and their density is controlled by equilibration with weak Si-Si bonds. The x>1.1 alloys behave like silicon nitride; the valence band changes towards N pπ-like, both Si and N DBs can arise, the Si DB can have a high density and prefers to be in its charged diamagnetic configurations.