Concentration dependence of the absorption coefficient for n− and p−type GaAs between 1.3 and 1.6 eV

The absorption coefficient α for GaAs at room temperature was determined in the spectral range from 1.3 to 1.6 eV by transmission measurements for 10⩽α⩽103 cm−1 and by a Kramers−Kronig analysis of the reflectance for α≳103 cm−1. Measurements were made on high−purity n−type samples, n−type samples with free−electron concentrations from 5×1016 to 6.7×1018 cm−3, p−type samples with free−hole concentrations from 1.5×1016 to 1.6×1019 cm−3, and p−type samples heavily doped with the amphoteric impurity Si. These data show that near the direct energy gap Eg the shape of the α−vs−photon−energy curve is strongly dependent on the impurity concentration.