Electronic Surface States and the Cleaned Germanium Surface

Abstract

The large $p$-type surface conductivity and field-induced surface conductivity of the cleaned germanium surface have been measured over the temperature range 77°-300°K. It is found that the surface conductivit and the field-induced surface conductivity are almost independent of temperature, varying by a factor of two over the temperature range investigated. The effect of oxygen, atomic hydrogen, and water vapor on the surface conductivity has also been observed. A qualitative two-dimensional band model is presented which correlates most of the experimental results. In this model, which is somewhat similar to the three-dimensional band model of graphite, there is a two-dimensional surface state band at the surface which overlaps in energy a two-dimensional valence band just beneath the surface. The states which form the surface state band are assumed to be perturbed out of the conduction band. The filling of these surface states with electrons out of the valence band gives rise to the observed $p$-type conductivity associated with the cleaned germanium surface.