Shallow defect states in hydrogenated amorphous silicon oxide

The theoretical cluster-Bethe-lattice method is used in this study to investigate the shallow defect states in hydrogenated amorphous silicon oxide. The electronic density of states (DOS) for the SiO2 Bethe lattice of various Si–O–Si angles, non-bridging oxygen Si–O, peroxyl radical Si–O–O, threefold coordinated O3 and Si–H bonds are calculated. The variation of the Si–O–Si bond angle causes the bandgap fluctuation and induces tail states near the conduction band minimum. The Si–O and Si–O–O bonds introduce shallow defect states in the energy gap near the top of the valence band. The Si–H bond induces a defect state, in the energy gap near the conduction band minimum, in a-SiOx with high oxygen concentration, but not low oxygen concentration. The O3 bond itself does not induce defect state in the energy gap. The O3+D− complex, formed by the O3 and threefold coordinated silicon, induces shallow state in the energy gap near the conduction band minimum. This defect state can explain the energy shift of photoluminescence of a-SiOx:H under annealing.