Effects of N⁺-implanted sapphire (0 0 0 1) substrate on GaN epilayer

We have investigated the effects of N⁺-implanted sapphire (0 0 0 1) substrate on a GaN epilayer grown by metal-organic chemical vapor deposition (MOCVD). As a result of implantation with 55keV nitrogen ions (N⁺) to a dose ranging from 1 × 10¹⁵ to 1 × 10¹⁷cm^-2 prior to GaN epilayer growth, the N⁺-implanted sapphire surface was chemo-physically modified and a thin disordered AlN phase was observed. The N⁺-implanted substrate's surface had decreased internal free energies during the growth of the GaN epilayer, and the misfit strain was relieved through the formation of an AlN phase on the N⁺-implanted sapphire (0 0 0 1) substrate. Crystallographical and optical properties of GaN epilayer grown on N⁺-implanted sapphire (0 0 0 1) substrate with the ion dose of 1 × 10¹⁶cm^-2 were found to be improved, indicating decreased internal stress and generation of dislocations in the GaN epilayer. The present results show that N⁺-implantation pre-treatment of the sapphire (0 0 0 1) substrate surface can be used to improve the properties of GaN epilayers grown by MOCVD.