Optical and spectroscopic characterization of GaAs passivated surfaces

The importance of the surface treatment for GaAs surfaces has been well established. The most relevant source of recombination centers lies just on the surface. GaAs-based devices are obvious subjects where surface treatments, involving both oxide removal and surface passivation, are so important for this rapidly evolving application. We have extensively tested some methods for treating the GaAs surfaces. A simple commercial GaAs:Zn 2.7 × 1018 cm-3 p-doped wafer has undergone different procedures: simple acetone/methyl-alcohol degreasing, a method that uses an anodic cell with (NH4)2S and a passivating P2S5(NH4)2S solution. Hydrochloric acid has been used as well, because of the well-known utility for GaAs oxide removal. Energy positions of EF and filled and empty surface density of states have been measured by scanning tunneling microscope spectroscopy. Photo-induced luminescence has been also used to study the role of the surface trap states after different surface treatments.