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 similar to 450-500 degrees 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 similar to 900 and 1000 degrees 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. Published by Elsevier B.V.