Reduction of Schottky barrier heights by surface oxidation of GaAs and its influence on DLTS signals for the midgap level EL2

Abstract

The barrier heights of Al-Schottky diodes formed on surface oxidized GaAs have been found to be smaller than those on as-etched GaAs. They recovered to the as-etched value when the samples were annealed, probably due to reduction of the surface oxide layer by Al. The barrier height of Au-Schottky diodes formed on surface oxidized GaAs depend on the oxidation conditions. These variations of the barrier height can be explained by differences of the oxide compositions and bonding strengths of the metal oxides (AlO, GaO etc.). In accordance with decrease of the barrier height, the DLTS (Deep Level Transient Spectroscopy) signal of the midgap level EL2 decreased and the signal peak shifted to a lower temperature even for the AuGaAs Schottky barrier. The decrease of the DLTS signal can be explained by a change of the occupation factor due to change of the reverse saturation current density.