An investigation of optically activated Si—SiO2interface states in metal-oxide-silicon structures

Transparent gate structures were fabricated by electron-beam evaporation of Sn-doped In2O3on oxidized p-Si substrates. The samples were oxidized at 1100°C in dry oxygen. No post-oxidation or post-electrode-deposition annealing was carried out. Admittance-voltage-frequency measurements were made under optical illumination. Interface state density distributions and hole and electron capture cross sections were obtained using the recently developed optical metal-oxide-semiconductor admittance technique. The experimental interface state density profile contained two peaked distributions, one near the valence band edge Ev, and the other near the conduction band edge Ec, Overlying a concave background. The peak near Ecwas sharper and the peak density was higher than in the Case of the peak near Ev. The capture cross section versus bandgap energy profile also displayed a peaked distribution for interface states under each of the peaks. With increasing illumination, the state density at the peak increased, the peak energy location moved closer to the respective band edge, and the capture cross section decreased. The experimental results show the presence of defects at unpassivated Si-SiO2interfaces, which exchange electrons/holes with the silicon bands under illumination.