Photoreflectance of GaAs and Ga_0.82Al_0.18As at elevated temperatures up to 600 °C

We report a modulation spectroscopy experiment on GaAs and Ga 0.82Al0.18As at elevated temperatures. Using the contactless electromodulation method of photoreflectance, the direct gaps (E0) of these materials have been observed from 77 K to 600 °C. The latter temperature is comparable to molecular beam expitaxy, metalorganic chemical vapor deposition, growth temperatures, etc. Our results are at the highest temperature yet reported for E0 (GaAs) in a reflectance experiment and the first observation of E0 (Ga1-xAl xAs) at elevated temperatures. From the latter, the Varshni coefficients [Physica 34, 149 (1967)] for Ga0.82Al0.18As were determined.