Localized States at the Conduction-Band Edge of Amorphous Silicon Nitride Detected by Resonance Photoemission

The Si LII,III absorption edge in amorphous silicon nitride (a-SiNiₓ:H) exhibits a Fano-type antiresonance just below threshold for x=1.20 and 1.40. At the same energy the valence-band photoemission cross section is resonantly enhanced in these samples for those features that carry an appreciable Si-$3s$-derived partial density of states. We argue that the Fano resonance involves Si-Si antibonding states at the bottom of the conduction bands that become localized as their number decreases with increasing nitrogen content compared to that of Si-N bonds.