Hydrogen incorporation in high hole density GaN:Mg

We investigate hydrogen passivation in heavily doped p-type GaN using electron paramagnetic resonance (EPR) spectroscopy. Samples include both conventionally grown GaN (10$^{19}$ cm$^{-3}$ Mg, 10$^{17}$ cm$^{-3}$ holes) and films grown by metal modulation epitaxy (MME), which yielded higher Mg (1-4x10$^{20}$ cm$^{-3})$ and hole (1-40x10$^{18}$ cm$^{-3})$ densities than found in conventionally grown GaN. The Mg acceptor signal is monitored throughout 30 minute annealing steps in N$_{2}$:H$_{2}$ (92{\%}:7{\%})) and subsequently pure N$_{2}$. N$_{2}$:H$_{2}$ heat treatments of the lower hole density films begin to reduce the Mg EPR intensity at 750 $^{o}$C, but quench the signal in high hole density films at 600 $^{o}$C. Revival of the signal by subsequent N$_{2}$ annealing occurs at 800 $^{o}$C for the low hole density material and 600 $^{o}$C in MME GaN. The present work highlights chemical differences between heavily Mg doped and lower doped films; however, it is unclear whether the difference is due to changes in hydrogen-Mg complex formation or hydrogen diffusion.