Hydrogen in III–V Semiconductors

ABSTRACTThe reversible introduction of atomic hydrogen into III–V semiconductors reduces the active concentrations of shallow donor and acceptor levels, as well as a variety of deep levels. Dissociation of the hydrogen-containing complexes by thermal annealing can restore the original active concentrations, and aid in the characterization of the complexes involved. Hydrogen is in-diffused at temperatures typically in the 150 to 300°C range, most simply from an H2 plasma.In GaAs, the III–V compound which has been subjected to the most hydrogenation studies, carrier concentrations are reduced (by up to many orders of magnitude) in both n- and p-type material. Hydrogen diffusion depths are dependent on dopant concentration, but for similar doping levels, diffusion is always deeper into p-type GaAs. In addition, the type of plasma exposure strongly influences the depth of H diffusion, with low frequency, direct exposure producing the greatest penetration depth. A variety of deep level defects in bulk material (including EL2) and in MBE-grown layers can be passivated, and partial passivation of interface-related defects in GaAs-on-Si has been demonstrated. Reactivation kinetics are dependent on the nature of the dopant or defect, with the passivation of p-GaAs being less stable than that of n-GaAs. Recent infra-red absorption studies have confirmed the formation of a donor-hydrogen complex in n-GaAs, in contrast to an As-H complex in p-GaAs. In GaAIAs, acceptors, donors, and the DX center have been passivated. In some cases, the defect passivation has greater thermal stability than that of the shallow levels, a property of potential benefit. Recently demonstrated applications of hydrogenation include an MBE GaAs MESFET with a hydrogenated channel, and a GaAs/GaAIAs double heterostructure laser with current guiding provided by resistive hydrogenated regions.