X-Ray Photoelectron Spectroscopic Analysis of the Oxide of GaAs

Oxides of GaAs grown using various oxidation processes were analyzed with X-ray photoelectron spectroscopy (XPS). Oxides investigated were the native (naturally grown or exposed to air), the chemical (grown in boiling deionized water) and the thermal (at 350°C and 500°C in dry oxygen) ones. With the use of a spectral deconvolution technique, all types of suboxides of both As and Ga including elemental arsenic were observed in addition to well-known As2O3 and Ga2O3. Elemental arsenic is considered to be one of the oxidized forms of GaAs. As2O5 was observed in the thermal oxides. In the chemical oxide and the native oxide grown in short exposure to air, elemental arsenic is the main component of oxide, while As2O3 is the dominant species in more highly oxidized films such as the thermal oxide. XPS data suggest that oxidation of As bonded in GaAs proceeds as GaAs→elemental As (As0)→As2O (As1+)→AsO (As2+)→As2O3 (As3+)→As2O5 (As5+). Oxidation of Ga bonded in GaAs advances as GaAs→Ga2O (Ga1+)→GaO (Ga2+)→Ga2O3 (Ga3+). Angle-resolved XPS measurements and semiquantitative analyses of these data were performed and an effective thickness of each oxide was also derived with simplified assumptions. The native and the chemical oxides were nearly stoichiometric. However, the thermal oxide was substantially Ga-rich due to desorption and evaporation of As2O3 from the surface during oxidation.