Structural evolution of GaN layers grown on (0 0 0 1) sapphire by hydride vapor phase epitaxy

GaN was grown directly on (0 0 0 1) sapphire by a two-step process using hydride vapor phase epitaxy (HVPE). Nucleation layers deposited on sapphire at ∼450–500 °C consisted of localized epitaxial wurtzite GaN nano-crystals. In between and above the epitaxial nano-crystals were randomly oriented wurtzite GaN nano-crystals. GaN islands of various sizes and shapes were formed, after annealing between ∼900 and 1000 °C, through a decomposition–redeposition process. Preferential growth of GaN occurred on the islands that had an epitaxial relationship with sapphire during the subsequent high-temperature overgrowth. Threading dislocations were observed in isolated GaN islands that were formed after annealing.

► GaN nucleation layers deposited using hydride vapor phase epitaxy consist of both epitaxial and randomly oriented wurtzite nano-crystals.
► GaN islands were formed after annealing, through a decomposition–redeposition process.
► Coalescence boundaries play a minor role in the formation of threading dislocations.