Depth dependence of silicon donor passivation and reactivation in hydrogenated GaAs

The depth dependence of silicon donor passivation and reaction in hydrogenated GaAs is directly determined for the first time by using 1000 Å layers of 10¹⁷ cm^-3 Si-doped GaAs, buried at various depths in undoped GaAs. Low-frequency hydrogen plasma exposure for 30 min at 250°C reduces the carrier density by only a factor of 3 in layers buried 3 μm deep, but by three orders of magnitude in layers buried 0.3 μm deep. Annealing at 400°C for 5 min restores 100% of the original carrier density in the 3-μm-deep layer but only 73% in the 0.3-μm-deep layer. Plasma exposure and 400°C annealing together do not improve the mobility in the molecular beam epitaxial samples at any depth. Hydrogen-related acceptors seen by photoluminescence account for these effects.