Oxidation and annealing of GaAs (100) studied by photoreflectance

Photoreflectance (PR) has until now been a technique used primarily for characterization of bulk electronic band structure in semiconductors. However, since reflectance is an interfacial phenomenon, PR should in principle be sensitive to surface treatment as well. The present work appears to be the first quantitative use of PR to measure the effects of surface treatment. In particular, PR spectra of air-oxidized and of annealed GaAs(100) are shown to be substantially different from those of the clean surface. Spectra at the E0 (1.4 eV) and E1 (3.0 eV) transitions respond quite differently to these treatments, and the differences are explained in terms of an optical interference phenomenon due to excitons that occurs only at E0. Effects of slow surface states have been observed with PR for the first time. The effective barrier between these states and the bulk decreases from 21±2 to 16± 2 meV upon air oxidation of the clean surface.