Near-surface QWS in GaAs: Recovery of emission efficiency via surface passivation by hydrogen and stability effects

The role of surface states in reducing the radiative efficiency of a GaAs/AlGaAs quantum well (QW), situated in proximity of the surface, has been investigated. The near-surface QW photoluminescence (PL) was utilized as a probe of the effects of room-temperature hydrogen irradiation and of the subsequent evolution of the system in time. The el-hhl PL at 1.4 K of various near-surface wells, differing in distance from the surface, was found to drop when the AlGaAs barrier was made thinner than 150 A, due to short-circuiting recombination processes at the surface. The data were interpreted in terms of electron and hole tunneling to surface states. The tunneling process showed saturation at medium-high laser power densities. A complete recovery of the emission in the near-surface QW was achieved by moderate irradiation of the samples at room temperature with a beam of 100-eV H ions. A study of the stability of the passivation effect - samples being investigated again after an eight-month-long exposure to air, or after annealing in vacuum - is indicative of important changes in the lifetimes of the different radiative and non-radiative processes associated with the well, due mainly to diffusion of hydrogen past the well depth. Room-temperature aging, however, does not seem to depassivate most of the surface states involved in tunneling. For the sample to be brought back to its original behavior, annealing in vacuum at temperatures above 400 °C was needed. Some indication that surface states are re-activated at a lower temperature than non-radiative centers inside the well was found.