Novel approach to the fabrication of a strain- and crack-free GaN free-standing template: Self-separation assisted by the voids spontaneously formed during the transition in the preferred orientation

A c-oriented GaN film was grown on a r-plane sapphire substrate by utilizing hydride vapor phase epitaxy. This non-typical orientational relation between the film and the substrate was possible by spontaneous transition in preferred orientation, and voids were spontaneously formed in an orientation-transition layer. This c-oriented thick GaN film was then self-separated from the substrate during cool-down process to room temperature after the growth. This intriguing phenomenon of the self-separation of crack- and strain-free GaN is attributed to the spontaneous formation of voids during the preferred orientation-transition, and suggests a novel method to fabricate crack- and strain-free GaN free-standing templates.