REORDERING AT THE GAS-PHASE POLYSULFIDE PASSIVATED GAAS(110) SURFACE

The structural and chemical changes of the GaAs(110) surface induced b y sequential processes of UV/O-3 exposure, HF etching, and gas-phase p olysulfide passivation were investigated by x-ray photoelectron spectr oscopy (XPS), low-energy electron diffraction (LEED), and thermal deso rption. Prior to any annealing, no samples showed any LEED patterns, a nd XPS indicated the presence of both As-S and Ga-S bonds. When the po lysulfide-passivated surface was annealed to 400 degrees C, a sharp ob lique LEED pattern started to emerge, which was accompanied by the des orption of S-As species. At the same time, XPS indicated that only a s ingle type of sulfide (S-Ga) remained on the surface. Further annealin g of the sample to 600 degrees C resulted in a complete removal of sul fur species from the surface and the appearance of a (2x1) LEED patter n. In contrast, no LEED pattern was observed from samples that had onl y been subjected to UV/O-3 treatment and HF etching up to an anneal te mperature of 600 degrees C, thus indicating the absence of any kind of ordered structure on these surfaces. The results suggest that sulfide assisted the reordering of the GaAs(110) surface; this is most likely a crucial factor in the improvement of the electrical properties of t he devices based on this surface. (C) 1996 American Vacuum Society.