Dependence of Si-SiO2 interface state density on oxide thickness in structures with ultrathin (79–227 Å) oxides

Admittance voltage characteristics of Si/79–227 Å SiO2/metal structures were measured in dark and under optical illumination in the frequency range of 30 Hz–100 kHz. For fabricating the structures, thermal oxidation was carried out in dry oxygen at 900 °C at 1 atm. The interface state versus band-gap energy profiles of the unannealed samples exhibited peaked distributions near the valence and conductance-band edges, overlying a concave background. The interface state density versus oxide thickness profile was observed to go through a minimum and a maximum instead of decreasing in a monotonic fashion.