CHEMISTRY AND STRUCTURE OF GAAS-SURFACES CLEANED BY SULFUR ANNEALING

A new method for cleaning and passivating GaAs surfaces, sulfur annealing, is proposed. The GaAs surfaces are exposed to sulfur atoms generated by an Ag/AgI/Ag2S/Pt electrochemical cell at elevated substrate temperatures without arsenic beam irradiation. The chemistry and structure of the GaAs surfaces cleaned by sulfur annealing are studied by synchrotron radiation photoemission spectroscopy and low energy electron diffraction (LEED). The S 2p and Ga 3d spectra indicate that Ga-S bonds are formed on the GaAs surfaces, where no oxides remain. 4 x 1 and 2 x 1 LEED patterns were observed for the surfaces with an average sulfur layer thickness of 0.15 nm and 0.24 nm respectively. The surface band bending is found to be reduced by 0.2-0.3 eV for the sulfur-annealed surfaces, but slightly increased for the conventionally cleaned surfaces with arsenic beam irradiation. We conclude that the surface cleaning and the submonolayer sulfur passivation can be attained simultaneously by sulfur annealing without arsenic beam irradiation. The method is promising for pre-cleaning the GaAs surfaces before semiconductor crystal growth and thin film deposition.