EFFECT OF HEAVY DOPING ON THE OPTICAL-PROPERTIES AND BAND-STRUCTURE OF GAAS

We have measured by spectral ellipsometry the pseudodielectric function epsilon(omega) of pure and heavily doped GaAs in the energy range 2-5.5 eV. A dependence of the E1, E1 + DELTA1, E0', and E2 critical-point energies and the lifetime broadening on doping has been observed. Amplitudes and phase angles for the corresponding critical points were also obtained. A difference between the behavior of n- and p-doped materials was found, especially concerning the magnitudes of critical-point energies and broadening parameters. The results are compared with second-order perturbation-theory calculations of the effect of substitutional impurities on the band structure of GaAs.