Compound semiconductor oxide antireflection coatings

We report the development of high quality, broad-bandwidth, antireflection (AR) coatings using the low index provided by wet thermally oxidized Al0.98Ga0.02As. We address the design criteria, fabrication, and characterizations of AR coatings composed of surface and buried oxide layers on GaAs. We show, using native-oxide dispersion data, that surface oxide coatings can be designed to offer a nearly zero minimum of reflectance and a reflectance of < 1% over bandwidths as large as 500 nm. Surface coatings having a reflectance minimum of 0.4% and a reflectance of < 1% over > 250 nm have been experimentally demonstrated at a design wavelength of 1 micrometer. Additionally, buried oxide coatings can be designed with an AlxGa1-xAs matching layer of any composition to exactly match the admittance of any substrate with effective index between 2.5 and 3.5. We have demonstrated buried oxide coatings, also designed for 1 micrometer, having a reflectance minimum of 0.4% and a reflectance of < 1% over 21 nm. The calculated optical scattering loss from measured roughness data indicates that reflectance minima as low as 10(-4) % are ultimately achievable with native-oxide antireflection coatings. [S0021-8979(00)01709-6].