Mechanism of Schottky barrier formation: The role of amphoteric native defects

Abstract

A correlation between the Fermi level pinning deduced from Schottky barrier heights and from electrical properties of irradiated III–V semiconductors is found. The correlation indicates that similar defects are responsible for the Fermi level stabilization in both cases. It is proposed that amphoteric native defects, i.e., the defects which change their electrical characteristics depending on the Fermi level position, play a dominant role in the processes leading to a Schottky barrier formation. A detailed analysis of metal–GaAs contacts shows that in this case the amphoteric defects responsible for the barrier heights are VGa (acceptor) and a donor complex AsGa+VAs. It is shown that for thick metal coverages two barriers are formed. A surface barrier determined by the charge associated with a native defect and the bulk barrier controlled by the bulk doping. The sum of the two barrier heights satisfies the Schottky condition for the interface, but it is the bulk barrier that determines the macroscopic electrical properties of the contact. The model explains the evolution of the Fermi level position at the interface observed for metal coverages varying in a broad range of thicknesses. The relationship of the present proposal to previous models of Schottky barriers is discussed.