Resolved Free-Exciton Transitions in the Optical-Absorption Spectrum of GaAs

Abstract

The optical-transmission spectrum of high-purity epitaxial GaAs has been studied at 2 K in the spectral region near the free exciton. Both resolved free-exciton transitions ($n=1, 2$) and impurity-induced-absorption features are seen. The energy separation $E_x\mathrm{}\left(1s\right)-E_x\mathrm{}\left(2s\right)=3.15\mathrm{}\pm 0.15$ meV observed for the $n=1, 2$ states of the transverse exciton provides an unambiguous value for the exciton binding energy [$E_x\mathrm{}\left(1s\right)=4.2\mathrm{}\pm 0.2$ meV], which agrees well with theory.