The post-annealing effects of GaN epilayer grown on N⁺-ion-implanted sapphire substrate

Sapphire substrates have been widely adopted to grow high quality GaN epilayer despite the large differences of lattice constant and thermal expansion coefficient between them. So, GaN or AlN buffer layer on the sapphire was indispensably introduced before the GaN epilayer growth. Moreover, a pretreatment process prior to the buffer growth has been known to play a critical role in improving the GaN overgrown layer. Nitridation is a general and simple pretreatment at high temperature in N₂ or NH₃ ambience. A post-annealing process was employed to decrease lattice strain through thermal treatment, and the electrical properties such as Hall mobility and carrier concentration were improved by this increase of crystallinity. These results showed that improvement of the GaN epilayer can be achieved by combination of N⁺-ion-implantation pretreatment of sapphire substrate and a suitable post-annealing process.