Theory of free-electron optical absorption in n-GaAs

Free-electron optical absorption of Se-doped GaAs at room temperature is calculated and compared with existing experimental data. In addition to the standard features the theory takes into account a non-parabolic character of the conduction band, a short-range component of the Se donor potential and a plasmon generation in the presence of donors. Deformation potential constants for the conduction and the valence bands are calculated using the empirical pseudopotential method. A value of C = -15.7 eV is obtained for the conduction band and shown to agree with existing hydrostatic and uniaxial stress experiments. Assuming no impurity compensation and using no adjustable parameters we successfully describe the experimental free-electron absorption in GaAs as a function of photon wavelength for samples with various donor densities.