Arsenic on GaAs: Fermi-level pinning and thermal desorption studies

Abstract

Arsenic overlayers are grown on freshly cleaved, clean GaAs(110) surface at room temperature and studied with ultraviolet and x-ray photoelectron spectroscopy. The coverage of As on the GaAs surface appears to saturate quickly, with saturation occurring at <10 L As exposure. The saturation coverage is estimated to be a monolayer of chemisorbed As and it pins the surface Fermi level at 0.55±0.05 eV above the valence-band maximum (VBM) for both n- and p-type GaAs. Upon annealing at 300 °C, the chemisorbed As overlayer is desorbed from the surface and the surface Fermi level shifts back almost to the bulk position [0.2 eV below the conduction-band minimum (CBM) for n-GaAs and 0.1 eV above VBM for p-GaAs; CBM and VBM are the bulk Fermi-level positions]. Since all the various models of Schottky barrier formation predict similar pinning positions, it is difficult to distinguish between them based solely on this present result. However, this result does emphasize the fact that excess As on the surface can be responsible for surface Fermi-level pinning. Furthermore, this result also shows that the ‘‘As capping’’ technique used for surface passivation of GaAs is extremely nonintrusive.