Density and Energy of Surface States on Cleaved Surfaces of Germanium

The channel technique has been successfully applied to measurement of the properties of cleaved germanium surfaces. A clean germanium surface is highly $p$ type with the Fermi level near the valence band at the surface. This is brought about by acceptor-like surface states close to the edge of the valence band with a density of at least 1.5×${10}^{12}$/${\mathrm{cm}}^2$. The density of these low-lying surface states decreases when the surface is exposed to oxygen. A comparison is made between results on cleaved surfaces and surfaces cleaned by ion bombardment.