Surface Conductance and the Field Effect on Germanium

Measurements of the steady-state surface conductance and the change in this conductance with transverse electric field (field effect) have been made on a free germanium surface as a function of the gaseous ambient. The results can be understood in terms of two sets of surface states: one dependent upon the gaseous ambient and with a large density and long time constants, probably located at the outer surface of an oxide layer, and the other a set with much smaller density but shorter time constants, probably located at the germanium-germanium oxide interface. The interface states consist of a discrete state with free energy 0.13-0.15 ev below the intrinsic Fermi energy and density 1-3×{}10¹¹ states/cm², and a small continuous distribution. There is also indication of a discrete state greater than 0.13 ev above the intrinsic Fermi energy. The measurements suggest that surface scattering effects become important for large barrier layers.