Freestanding high quality GaN substrate by associated GaN nanorods self-separated hydride vapor-phase epitaxy

This work proposes a method for fabricating 2 in. freestanding GaN substrates of high crystallographic quality and low residual strain. Arrays of GaN nanorods with sidewalls coated with silicon dioxide (SiO₂) were randomly arranged on the sapphire substrate as a growth template for subsequent hydride vapor-phase epitaxy (HVPE). The passivation of the sidewalls coated with SiO₂ prevents the coalescence of GaN grains in spaces between the rods, causing them to grow preferentially on the top of individual rods. The proposed method significantly improves GaN crystal quality and results in self-separation from the underlying host sapphire substrate due to the relaxation of thermal strains in the HVPE cooling-down process.