Accumulation of Implanted Hydrogen at the Superlattice/Substrate Interface

A GaAs-AlAs superlattice grown on an-undoped GaAs substrate has been implanted with 300 keV protons to a fluence of 1E16/cm2. The implanted hydrogen and the deposited Al atoms have been depth profiled using secondary ion mass spectrometry (SIMS). Measurements of the as-implanted sample show that the hydrogen depth distribution is similar to that found previously with proton implants into bulk GaAs. Near the surface, the Al depth profile exhibits an alternating pattern characteristic of the superlattice compositional pattern. Annealing the sample, at temperatures from 300 to 700 C for a period of 20 minutes, causes the hydrogen to redistribute itself both towards the surface and deeper into the crystal. However, rather than diffusing into the substrate as in bulk GaAs, the SIMS profiling shows the hydrogen stopping and accumulating at the superlattice/substrate interftace. The hydrogen density at the interface is quite significant and, even after a 700 C anneal, is still above 1E18/cc.