Correlation between Surface Structure and Surface States at the Clean Germanium (111) Surface

Abstract

A transition from a 2×1 to an 8 structure on the ultrahigh-vacuum-cleaved germanium {111} face during heat treatment below 350°C makes germanium particularly well suited as a material for investigating a possible correlation between surface states and surface structure. Individual studies of either the electrical or structural properties of this surface have been made over a number of years, but the present experiment was designed to make both the structural and electrical measurements ``simultaneously'' on the same surface. In the present experiment both surface state density as calculated from surface conductivity and dc-field effect, and surface structure as characterized by symmetry and spot intensities of the LEED pattern were determined at 30°C as a function of heat treatment over the temperature range 30° to 300°C. The structural changes are accompanied by parallel changes in surface conductivity and field effect mobility. It is concluded that at cleaved germanium surfaces the surface states are essentially determined by the two-dimensional surface structure rather than domain boundaries or surface defects. A model which correlates different surface state distributions with the 2×1 and the 8 germanium superstructures allows the description of the present results. This is the first time that changes in surface state distributions have been directly correlated with changes in the two-dimensional surface structure.