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A synchrotron radiation photoemission study of the deposition of titanium on an oxidized GaAs (100) surface

The evolution of a titanium overlayer deposited on an oxidized GaAs(100) surface has been studied using synchrotron radiation photoemission spectroscopy. Experiments were carried out on clean GaAs surfaces which were subsequently oxidized in air to give a coverage of approximately one monolayer of oxide. These surfaces were prepared by the thermal decapping of a protective As overlayer in ultra-high vacuum (UHV). The subsequent deposition of submonolayer coverages of titanium resulted in the complete reduction of the native Ga and As surface oxides and the formation of a TiOx (1<x<2) metallic overlayer. The inherent surface sensitivity and resolution of the photoemission technique allowed details of the sequence of oxide removal to be investigated. The authors study would suggest that the interface formed in this way is extremely abrupt with no significant interdiffusion across the metal-semiconductor interface detected by the photoemission studies. This observation is in sharp contrast with similar studies for the same metal deposited on an atomically clean GaAs surface and on a heavily oxidized GaAs surface, both which exhibit strong out-diffusion of Ga and As atoms into the metal overlayer.