Rapid Mg substitution to Ga-sites and slow defect recovery revealed by depth-resolved photoluminescence in Mg/N-ion-implanted GaN

Toward p-type GaN formation by Mg ion implantation (I/I) applicable to devices, depth-resolved photoluminescence (PL) revealed key behaviors during activation annealing for precise profile control, such as Mg substitution into Ga-sites (MgGa) and recovery of I/I defects. Depth profiles of the MgGa acceptor concentration were measured for Mg-I/I and Mg/N-I/I samples after ultra-high-pressure annealing at 1300 °C for 1–60 min. The cycle of low-damage dry etching and PL measurement was repeated over the I/I depth, and the MgGa concentration was estimated at each depth based on the calibration curve for the PL intensity ratio between acceptor-bound excitons (A0XA) and free excitons (FXA). In the region deeper than the I/I peak of 0.3 μm, almost all of the Mg atoms rapidly substituted into Ga-sites during the short annealing process. By contrast, the Mg substitution ratios in the shallower region were low when the annealing process was short but were improved by the sequential N-I/I. The low substitution ratio can be explained by MgGa bonding with nitrogen vacancy (VN)-related defects, while the implanted N-ions can compensate them. The PL intensity near the mean implantation depth of Mg/N-I/I was gradually improved as the annealing duration was increased to 60 min, indicating a slow reduction of nonradiative recombination centers. Simultaneously, the green luminescence associated with the VN-related defects decreased in intensity with increasing annealing time. Therefore, the main effect of prolonging annealing is the enhancement of slow defect recovery rather than enhancement of the Mg substitution as a fast process.