Surface States on Silicon and Germanium Surfaces

Abstract

Interface states are found in the upper half of the energy gap of silicon and germanium. On weakly oxidized surfaces, they lie 0.42 and 0.13 ev above the intrinsic position of the gap with approximate densities ${10}^{11}$ to ${10}^{12}$ and ${10}^{10}$ to ${10}^{11}$ for silicon and germanium, respectively. On well-oxidized surfaces, interface states are found approximately 0.44 to 0.48 ev and 0.18 ev above the intrinsic position of the gap with densities of around ${10}^{12}$ and ${10}^{11}$ to ${10}^{12}$ for silicon and germanium, respectively. At large bias voltages, high electric fields exist in the oxide film. Changes in the structure of the interface states in the upper half of the gap of silicon are found. A model is given which can account for the experimental observation.