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 less than or equal to x less than or equal to 0.97), oxidation temperature (400 less than or equal to T less than or equal to 500), and carrier gas purity. Index values range from n = 1.490 (x = 0.9, 400 degrees C) to 1.707 (x = 0.3, 500 degrees C). The oxides are shown to adsorb moisture, increasing their index by up to 0.10 (7%). Native oxides of AlxGa1-xAs (x less than or equal to 0.5) have index values up to 0.27 higher and are less hygroscopic when prepared with a small amount of O-2 in the N-2+H2O process gas. The higher index values are attributed to a transition from a hydroxide to a denser (AlxGa1-x)(2)O-3 oxide phase. (C) 1999 American Institute of Physics. [S0003-6951(99)00434-9].