Passivation of Shallow and Deep Levels by Hydrogen Plasma Exposure in AlGaAs Grown by Molecular Beam Epitaxy

We report on the effects of exposure to a hydrogen plasma (hydrogenation) and of thermal annealing (dehydrogenation) on shallow and deep levels in direct-gap AlGaAs:Si grown by molecular beam epitaxy. Photoluminescence (PL) experiments show that hydrogenation results in the passivation of shallow levels, thus confirming the data of capacitance-voltage measurements, while deep-level transient spectroscopy shows that ME5, ME6 and DX centers are passivated by hydrogenation. Dehydrogenation at 420°C results in an almost complete recovery of the free electron concentration, and restores, to a significant extent, only the DX center. The study of samples grown at different temperatures shows that the significant increase of the PL efficiency after hydrogenation and its decrease after dehydrogenation are consistent with the passivation of the ME5 and ME6 levels and with their partial reactivation, respectively.