Elemental arsenic in the natural oxide on the MBE GaAs surface

Abstract

The thickness, elemental and chemical compositions of the native oxide naturally formed on a perfect GaAs(1 0 0) crystal grown by MBE have been studied by Auger electron spectroscopy (AES) and electron energy-loss spectroscopy (EELS) to specify the oxidation mechanism and to confirm or reject the questionable presence of elemental arsenic in the natural oxide. Elemental arsenic (Aso) arising in the oxidation process due to reduction of As2O3 by the GaAs substrate was revealed at the Auger energy of 1225.8 eV and shown to reach ~16 at% of the oxide whose thickness was determined to be ~4 nm. Aso was shown by EELS to form a segregate with the plasmon energy of 18.1 eV. Room temperature oxygen diffusivity through the finally formed oxide layer was estimated to be low enough (D < 10−21 m2/s) to explain retention of the Aso in the deepest oxide layers where it cannot oxidize again or diffuse away. The studied natural oxide was shown to have a layered nanostructure consisting of a cap As2O3 layer (~1 nm), a core oxide layer containing a Ga2O3/As2O3 mixture (~2 nm) enriched in Ga by a factor of 1.5, and a deep interface layer of elemental arsenic (~1 nm).