Nonhydrogenic Exciton and Energy Gap of GaAs

Abstract

The free-exciton series $n=1,2,3\mathrm{}$ in high-purity GaAs has been observed in photoluminescence and photoconductivity. The $n=1\mathrm{}$ peak shifts upon changing the excitation level because of free-carrier screening. Anisotropy and exchange effects as well as two valence bands must be included to interpret the series spectrum of this Wannier-like exciton. New values are derived for the band gap at 1.6 K ($E_g=1.5189\mathrm{}\pm 0.0001$ eV) and for the $n=1\mathrm{}$ excitonic binding energy [$E_X\mathrm{}\left(1s\right)=3.77\mathrm{}\pm 0.05$ meV].