The effect of surface oxygen on the intermixing and Schottky barrier at GaAs(110)–Au interfaces

Abstract

The effect of placing controlled amounts of oxygen on the clean, cleaved (110) surface of GaAs before exposure to Au has been investigated with ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy (XPS). We studied: (a) the shape of the Ga-3d level and changes of Ga (or As) intensity with oxygen and subsequent Au deposition; (b) the position of the Ga-3d core level, with special regard to the surface or interface Fermi level (Efs), as a function of oxygen and Au coverages; and (c) the valence band structure (where both oxygen and Au provide strong characteristic structure). For chemisorbed oxygen coverages of a small fraction up to 1 monolayer (ML) or above the Au:GaAs intermixing and Ef shifts are significantly reduced. For the p-type sample, after much less than 1 ML of oxygen, the maximum rise of Efs is suppressed as Au is added; after 107L exposure Efs remains stationary until approximately 1 ML of Au is deposited; for high oxygen coverage (≥108L), the oxygen appears to effectively retard the Au–GaAs interaction up to 10 ML of Au coverage. The width of the Ga-3d core level increases monotonically with increased oxygen exposure. With 1010L exposure of oxygen, the Au coverage necessary to drop the Ga intensity to 1/e of its value on the oxidized surface is decreased to 4 ML, instead of 6 ML for the unoxidized surface. Supporting evidence from XPS spectra further demonstrates the intermixing is reduced between Au and GaAs by oxygen. The valence band structure shows the Au is dispersed on the oxidized surface. The results show that, for GaAs surfaces with a few tenths to above 1 ML of oxygen (before Au is deposited and with no annealing), the oxygen–GaAs interaction inhibits Au intermixing with GaAs. It causes a more abrupt interface than the case without oxygen.