Surface States on Silicon and Germanium Surfaces

Abstract

On silicon and germanium, steady-state and nonsteady-state $p$-type inversion layer conductance measurements can be understood in terms of two sets of surface states: one with a great density outside the oxide and the other with a smaller density at the semiconductor-semiconductor oxide interface. The interface states in silicon and germanium lie 0.455 and 0.138 ev, respectively, below the middle of the gap. There may also be interface states in the upper half of the gap; however, for their determination, measurement on $n$-type inversion layers would have to be made. The density of the interface states in silicon is about 1.4\ifmmode\times\else\texttimes\fi{}${10}^{12}$ states/${\mathrm{cm}}^{2}$; the density in germanium is one-tenth this value. Various mechanisms of charge transfer through the oxide film are considered and compared with experimental data.