Influence of Temperature on Anodically Grown Native Oxides on Gallium Arsenide

A native oxide film is grown on GaAs by anodically oxidizing GaAs in a mixed solution consisting of aqueous tartaric acid and ethylene glycol. A homogeneous oxide film up to 8000 angstrom thick is obtained with a linear thickness-voltage dependence of 19.5 angstrom/V. The as-grown oxide is highly transparent in the near infrared and the visible light regions. The refractive index is almost constant in the near infrared region, and it weakly depends on the wavelength in the visible light region changing from 1.7 to 1.9. In the u.v. region, the oxide becomes less transparent and is completely opaque for wavelengths shorter than 0.22 mu m. The oxide is very stable and almost no detectable changes regarding oxide properties, structure, and composition occur below 350 degrees C However, the oxide begins to decompose above 350 degrees C first by releasing water. The oxide decomposition most rapidly proceeds around 450 degrees C mainly by vaporizing water and arsenic oxide. It continues up to 700 degrees C resulting in a pure gallium oxide. The refractive index of the decomposed oxide is fairly constant around 1.5 over the wide wavelength region from visible light to near infrared. The decomposed oxide is believed to be beta-Ga2O3. By heat-treatment above 650 degrees C the surface of GaAs becomes rough and a new layer is formed at the oxide-GaAs interface. This interface layer is completely arsenic depleted and has a Ga:O ratio of 2:1. The highest temperature to which the anodically oxidized GaAs can be heat-treated is approximately 650 degrees C. As a means for increasing this temperature limit, a double oxide structure consisting of the anodic oxide film and a SiO2 film is investigated. By coating GaAs with double oxide films consisting of a 500 angstrom thick anodic oxide film and a 2000 angstrom thick SiO2 film, GaAs can be heat-treated at 800 degrees C for 2 hr without degradation of the GaAs surface.