EXTINCTION OF INFRARED RADIATION BY OXIDIZED AND HEAT-TREATED GAAS

Extinction of ir radiation at wavelength from 0.9 to 25 mu m by therma lly oxidized GaAs as well as by GaAs with and without protective layer s after heat treatments in various environments is studied. For sample s treated in air, two stages corresponding to a large increase of the total extinction are found near 450 and 750 degrees C, respectively. T he extinction spectrum at the first stage is determined by an intermed iate As-rich layer placed between the cap layer and the non-distorted GaAs decreasing the transmission over the whole spectral range studied . An extra absorption band near 5.5 mu m is attributed to a surface pl asmon (Frohlich mode) in As precipitates. At lambda < 2 mu m, a contri bution is detected owing to absorption by EL2-like and As-Ga-related d efects. Their average concentration in the intermediate layer is estim ated as approximate to 4 x 10(20) cm(-3). The second stage of ir extin ction is explained in terms of As evaporation from the sample surface which leads to the formation of a nondense GaAs layer containing voids .