Atomic-scale investigation of implanted Mg in GaN through ultra-high-pressure annealing

An area selective doping via ion implantation is a key technology to realize gallium nitride (GaN) based energy-efficient power devices; however, conventional annealing leads to the formation of numerous Mg-enriched defects, which results in inefficient p-type activation. Recent invention of ultra-high-pressure annealing (UHPA) has enabled a significant improvement of p-type activation efficiency. In this study, we investigated the formation of Mg-enriched defects in Mg implanted GaN followed by annealing under both conventional atmospheric pressure and ultra-high-pressure. Unlike the conventional annealing, UHPA leads to much lower number density of Mg-enriched defects. Correlative scanning transmission electron microscopy (STEM), atom probe tomography (APT), cathodoluminescence (CL) and secondary ion mass spectrometry (SIMS) analyses have shown that the number density of Mg-enriched defects are substantially suppressed by the UHPA. The dissolved Mg concentrations in the GaN matrix for both the conventional and the UHPA samples are almost at the same value, approximately 2 × 1018 cm-3; however, the UHPA sample shows over one order of magnitude stronger intensity of donor-acceptor-pair (DAP) emission than the conventional one. Thus, the implanted Mg is effectively activated as acceptors through the UHPA technique.