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].
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Bimberg et al. (1972) studied this question.
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