Refractive index and hygroscopic stability of AlxGa1−xAs native oxides

We present prism coupling measurements on AlxGa1−xAs native oxides showing the dependence of refractive index on composition (0.3⩽x⩽0.97), oxidation temperature (400⩽T⩽500), and carrier gas purity. Index values range from n=1.490 (x=0.9, 400 °C) to 1.707 (x=0.3, 500 °C). The oxides are shown to adsorb moisture, increasing their index by up to 0.10 (7%). Native oxides of AlxGa1−xAs (x⩽0.5) have index values up to 0.27 higher and are less hygroscopic when prepared with a small amount of O2 in the N2+H2O process gas. The higher index values are attributed to a transition from a hydroxide to a denser (AlxGa1−x)2O3 oxide phase.