Electron spin resonance and hopping conductivity of a-SiO x

Abstract

Amorphous SiO x-layers with O < x < 2 have been prepared by evaporation of Si at oxygen pressures of 10 −6 … 10 −3 mbar. The composition of the samples was determined by proton backscattering. The band gap, derived from optical measurements, increases with rising oxygen content relatively little at first and the main enhancement occurs above x = 1.5. The ESR spectrum consists of two structures: (1) a relatively broad line A with g-value and linewidth depending considerably on composition, particularly after irradiation with He +-ions of 250 keV energy, and (2) a narrow line B with g ≈ 2.0001 which corresponds to the E′-center in SiO 2 and increases in intensity with rising oxygen content. The properties of the broad line A can be described by a superposition of 3 lines with different g-values and linewidths. The hopping conductivity after He +-irradiation decreases strongly with increasing oxygen content indicating that the E′-center does not contribute to the hopping transport.