Nonhydrogenic exciton and energy gap of GaAs

The free-exciton series n=1,2,3 in high-purity GaAs has been observed in photoluminescence and photoconductivity. The n=1 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 (Eg=1.5189±0.0001 eV) and for the n=1 excitonic binding energy [EX(1s)=3.77±0.05 meV]. © 1972 The American Physical Society.