HYDROGEN-DONOR-INDUCED FREE-EXCITON SPLITTING IN GAAS

Liquid-helium photoluminescence spectra have been taken in nominally undoped, donor-free GaAs grown by molecular-beam epitaxy and exposed to increasing doses of hydrogen irradiation. The narrow single free-exciton line observed in the untreated sample evolves into a broader doublet in the hydrogenated sample in the same way as was observed in high-purity GaAs on going from p-type to weakly n-type material. This behavior is highly suggestive of the activation of an exciton-polariton scattering mechanism by neutral donors, and provides an argument, in addition to existing experimental and theoretical evidence, in favor of a hydrogen-induced donorlike state. Measurements at different exciting wavelengths and bath temperatures support the model.