Photon-stimulated tunnelling of electrons in SiO2: Evidence for a defect-assisted process

Photon-stimulated tunnelling (PST) of electrons at Si-SiO2 and SiC-SiO2 interfaces is shown to be insensitive to the density and energy distribution of electrons in the semiconductors. Instead, the observed relation of PST to the type of the oxide layer indicates a defect level in the oxide as the initial state of electrons contributing to PST. The defect's energy level was found to be positioned 2.8 eV below the conduction band of SiO2, the defect density increasing with silicon enrichment of the SiO2. The observed correlation between PST yield and dark conductance of the oxide suggests the isolated defect states to be involved in the high-field electron transport of SiO2 layers.