COMPARATIVE-STUDY OF THE OXIDE-GROWTH MODE ON GAAS(111) AND (111) SURFACES - IMPLICATIONS FOR DIRECT OXIDE ELECTRON-BEAM WRITING

The growth mode of oxide films (< 3 nm thick) obtained by electron beam oxidation is investigated on a wide range of polar GaAs{111} surfaces. Information is derived from a quantitative analysis of the Auger intensities for different oxidation models. Oxidation is always found to progress by a layer-by-layer mechanism with separate Ga and As oxide phases. The Ga-oxide growth is nearly insensitive to the starting surface, whereas a clear dependence is observed in the evolution of the As signal. Only a small fraction of the As atoms initially contained in each monolayer (ML) of GaAs{111} remains embedded in the Ga oxide; this fraction is zero, one-sixth or one-third of 1 As ML, for each oxide layer depending on the perfection of the initial surface. Therefore, this oxidation model supports previous indications that the elemental As often detected at the oxide/GaAs interface could not be formed during the oxidation process, but rather it is due to anion inclusions in the bulk which segregate at the interface.