The oxidation of GaAs(1 0 0) surfaces under atmospheric pressure conditions studied in real time using dynamic reflectance anisotropy spectroscopy at 2.6 and 4 eV

Using real-time, dynamic reflectance anisotropy spectroscopy (RAS) at both 2.6 eV and 4.0 eV, we demonstrate that an anisotropic oxide will form on As rich c(4 × 4)/d(4 × 4) GaAs surfaces when exposed to moisture- free air diluted in inert gases in a metal organic chemical vapour deposition (MOCVD) reactor, and that the initial c(4 × 4)/d(4 × 4) structure effects the resulting optical anisotropy of the oxide. This was achieved by investigating how the RA signals at 2.6 eV and 4 eV of annealed GaAs (1 0 0) surfaces evolve relative to the as-etched and as-annealed signals when exposed to oxygen. It is found that while the 2.6 eV response, which is known to be associated with the As dimers, degrades to pre-process levels indicating their destruction, the 4 eV signal, stabilizes at an intermediate, permanent level, suggesting the formation of an anisotropic oxide film whose structure is determined at least in part, by the initial c(4 × 4)/d(4 × 4) surface.