OPTICAL AND SPECTROSCOPIC CHARACTERIZATION OF GAAS PASSIVATED SURFACES

The importance of the surface treatment for GaAs surfaces has been wel l established. The most relevant source of recombination centers lies just on the surface. GaAs-based devices are obvious subjects where sur face treatments, involving both oxide removal and surface passivation, are so important for this rapidly evolving application. We have exten sively tested some methods for treating the GaAs surfaces. A simple co mmercial GaAs:Zn 2.7 x 10(18) cm(-3) p-doped wafer has undergone diffe rent procedures: simple acetone/methyl-alcohol degreasing, a method th at uses an anodic cell with (NH4)(2)S and a passivating P2S5/(NH4)(2)S solution. Hydrochloric acid has been used as well, because of the wel l-known utility for GaAs oxide removal. Energy positions of E(F) and f illed and empty surface density of states have been measured by scanni ng tunneling microscope spectroscopy. Photo-induced luminescence has b een also used to study the role of the surface trap states after diffe rent surface treatments.