Hexagonal growth spirals on GaN grown by molecular-beam epitaxy: Kinetics versus thermodynamics

GaN grown by molecular-beam epitaxy on Ga-polar GaN templates prepared by metal organic chemical vapor deposition shows a variety of morphologies that depend on defects and growth conditions. We measured the mean terrace widths of hexagonal growth spirals or hillocks versus ammonia and Ga fluxes and substrate temperature. The measurements were compared to a near equilibrium model of the growth. The results indicate that under excess Ga growth conditions, Ga-polar GaN(0001) has a mean step-edge energy of 0.27 eV/Å.