Hydrogen in III–V Semiconductors

The 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 H 2 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.