Optical constants of (Al0.98Ga0.02)xOy native oxides

We report the optical constants of oxidized crystalline and low-temperature-grown (LTG) Al0.98Ga0.02As films, as determined by variable angle spectroscopic ellipsometry. Data were acquired at three angles of incidence over 240-1700 nm and fitted to a Cauchy dispersion function. For oxidized crystalline material, we observe a variation in the real index of +/-0.5% for layer thickness variations of +/-6%. We show that upon oxidation, LTG material can expand by >25% while crystalline material contracts by <2%. Atomic force microscopy analysis indicates thickness-dependent variations in the oxide microstructure. Additionally, an optical scattering loss of 2.1 X 10(-4)%/pass is calculated based on surface roughness measurements for a thin layer of oxidized crystalline material. (C) 1998 American Institute of Physics. [S0003-6951(98)03550-5].