Determination of silicon-silicon dioxide interface state properties from admittance measurements under illumination

For the present investigation n-Si/SiO2/In2O3 transparent gate structures were fabricated by electron-beam evaporation of a tin-doped indium oxide layer on thermally oxidized silicon. Admittance measurements were carried out in dark and under three different levels of illumination. A comprehensive technique has been presented for obtaining interface state density distribution from illuminated capacitance data as well as from illuminated conductance data, and hole and electron capture cross sections from the latter. This technique includes a procedure for identification of the dominant quasi-Fermi level (imref) under illumination for determination of the state energy level, three independent methods for evaluating the imref separation from measured data, and a procedure for ascertaining whether electron or hole exchange is the source of a set of Gp/ω vs V or ω characteristics. The interface state density distribution of unannealed structures exhibited two peaked profiles. One peak was located about 0.36–0.41 eV above the valence-band edge, while the other was located about 0.30–0.17 eV below the conduction-band edge. The peak magnitude was found to increase with the illumination intensity and the peak position moved towards the respective band edge. Electron capture cross sections of states in the upper band gap half were found to be in the range of 10−18–10−20 cm2, and hole capture cross sections of states in the lower band gap half in the range of 10−15–10−16 cm2. Both σe and σh were found to vary with band-gap energy and illumination level.