Effect of heavy doping on the optical properties and band structure of GaAs.

Abstract

We have measured by spectral ellipsometry the pseudodielectric function \ensuremath{\varepsilon}(\ensuremath{\omega}) of pure and heavily doped GaAs in the energy range 2--5.5 eV. A dependence of the ${\mathrm{E}}_{1}$, ${\mathrm{E}}_{1}$+${\mathrm{\ensuremath{\Delta}}}_{1}$, ${\mathrm{E}}_{0}^{\ensuremath{'}}$, and ${\mathrm{E}}_{2}$ 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.