Photoemission of Electrons from Silicon into Silicon Dioxide. Effects of Ion Migration in the Oxide

Abstract

Photoemission of electrons from silicon into SiO2 has been used as a tool to study changes at the silicon-SiO2 interface which result from the application of high electric fields at elevated temperature. Before treatment the photoemission threshold energy for electrons from silicon into SiO2 is 4.22 eV. After applying a dc voltage across the oxide at elevated temperature, with polarity such that the silicon is negative, there are significant changes in the photoemission spectrum. A new low-energy branch appears which gives a threshold energy around 3.05 eV. This is believed to be due to the formation of a degenerate n-type surface. Light absorption by electrons in the conduction band becomes important, and there is a corresponding contribution to the photoemission current. Semiquantitative arguments are advanced to show what the charge distribution in the oxide must be to account for the experimental results.