The optical absorption coefficient of high-resistivity gallium arsenide has been measured over the range of photon energy 0.6 to 2.75 eV, at temperatures from 10 to 294°K. The main absorption edge shows a sharp peak due to the formation of excitons. The energy gap and exciton binding energy are deduced from the shape of the absorption curve above the edge. Their values at 21°K are 1.521 and 0.0034 eV, respectively. Absorption from the split-off valence band is observed, the spin-orbit splitting being 0.35 eV at the center of the zone. The exciton line shows unexplained structure on the low-energy side. Application of a stress splits the exciton line by 12 eV per unit [111] shear, and shifts it by -10 eV per unit dilation. Absorption due to the ionization of deep-lying impurity levels is observed, with thresholds at 0.70, 0.49, and 0.27 eV from the main absorption edge.

• Received 26 March 1962

DOI:https://doi.org/10.1103/PhysRev.127.768