To determine accurately the absorption coefficient of GaAs n-doped crystals, we developed an apparatus which permits simultaneous measurement of the coefficients of absorption K and reflection R12 of samples. We have determined with high precision that the absorption edge is exponential, and thus brought to light that not only the concentration of the nt impurities, but also their nature changes the slope of the curve log K plotted as a function of the energy. We attribute this to stresses produced in the lattice by impurity atoms. Finally, we note that the reflection coefficients vary greatly from one sample to another.
JACQUES LEFEVRE, DANIEL BOIS, PIERRE PINARD, FRANÇOIS DAVOINE, and PIERRE LECLERC, "Influence of Impurities on the Optical Absorption Edge of Gallium Arsenide from 297° to 4°K," J. Opt. Soc. Am. 58, 1230-1232 (1968)