Photoemission studies of barrier heights in metal–semiconductor interfaces and heterojunctions

The technique of photoelectron spectroscopy has contributed tremendously to our knowledge on the properties of semiconductor interfaces, in aspects such as the electronic structure at the interface, relating to band bending and the evolution of transport barriers such as the Schottky barrier and the heterojunction band offset. This paper describes recent progress in this field, concentrating on metal contacts to wide band gap semiconductors, and the question of band offset engineering through intralayers. Some of the pitfalls of the technique are pointed out, such as in cases where the assumption of an equilibrium situation and/or the presence of a flat band condition in overlayers is not fulfilled. This is particularly important with reference to the "interface dipole" interpretation of results from intralayers in GaAs/AlAs junctions, which are discussed in the light of recent experiments