Hydrogen activated radiative states in GaAs/GaAlAs heterostructures and InGaAs/GaAs multiquantum wells

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Abstract
Direct observation of optical emission from H-related complexes in molecular beam epitaxy grown bulk GaAs and GaAlAs, as well as InGaAs/GaAs strained multiquantum wells (MQWs), is obtained from liquid He photoluminescence experiments. Hydrogenation is achieved by low-energy ion irradiation from a Kaufman source. The volume incorporation of hydrogen, for equal treatment, is dependent upon the density of impurities and defects where H can bind. For moderate H treatment, in addition to passivation of shallow acceptors, in GaAs we observe novel emission bands, δ, peaking at 1.360, and γ, peaking at 1.455 eV. After heavy hydrogen treatment in GaAs of low radiative efficiency−even p type originally−there appears a deeper structure α at ∼1.20 eV, of the kind known for ‘‘internal’’ transitions in the Ga vacancy-donor complex. Equivalent bands are found in bulk GaAlAs and also in InGaAs/GaAs MQWs. The results allow an approximate estimate of the various optically active Ga-vacancy levels, as affected by the different degrees of hydrogenation of the dangling bonds, and a comparison with theoretical values. Moreover, they provide evidence for the creation of a H-related donor whose binding energy is of order 25 meV. Finally, the γ band is suggestive of a transition between localized conduction and valence states associated with the local distortion that is introduced in the lattice when H binds to impurities, defects, and lattice atoms.