Admittance measurements of Si-SiO2 interface states under optical illumination

Abstract

A new experimental technique is presented for the investigation of the localized electronic states at the silicon-silicon dioxide (Si-SiO2) interface, in which the ac conductance and capacitance of metal-oxide semiconductor structures is measured as a function of bias voltage and measurement frequency in the presence of a uniform background of optical illumination. The illumination is of photon energy in excess of the silicon energy gap, and provides for the photogeneration and supply of minority carriers to the silicon surface. The density of interface states and their capture cross sections for both majority and minority carriers can be obtained by this method, as well as possible dependencies of the cross sections on electric field at the semiconductor surface. Results obtained by conductance and capacitance measurements under illumination are in agreement with each other, and the capture cross section for minority carriers (electrons in our case) is observed to fall with increases in interface state energy towards the conduction band edge, in agreement with other workers.