On interfacial charges in the oxide layer of mis-type Ag- and Au- n GaAs Schottky barriers

Fixed interfacial charges in MIS type n-GaAs Schottky barriers were investigated by measuring the flatband voltage as a function of the oxide layer thickness in the range of 2-20 nm. The linear relationship obtained allowed the determination of the sign, the location and the density of these charges. In contrast to Si, negative charges were found here. They were located at less than 2 nm from the interface. From the dependence of the charge density on the annealing temperature the conclusion was reached that excess As at the oxide semiconductor interface is at the origin of these charges. The observed changes in work function difference at the interface caused by the annealing support a recent Schottky barrier theory developed by Woodall and Freeouf.