Homoepitaxial growth of gallium nitride films using seeded supersonic molecular beams

Homoepitaxial GaN thin films were grown on MOCVD GaN(0001)/A1N/6H-SiC substrates using NH3, elemental Ga and TEG. The GaN growth kinetics were probed using NH3-seeded and TEG-seeded supersonic molecular beams. A GaN surface kinetics model for growth using NH3 and elemental Ga was fitted with the data to find the zero-coverage NH3 sticking coefficient. Growth rates measured under NH3-limited conditions using hyperthermal NH3 beams with kinetic energies of 0.08--1.8 eV indicate decreasing nitrogen incorporation efficiency with increasing incident kinetic energy. The results indicate that NH3 chemisorption on GaN(0001) is unactivated and occurs via a precursor-mediated pathway. The surface morphology is controlled by the Ga surface diffusion length, which in turn, is controlled primarily by the GaN growth rate. Scaling analysis indicates surface diffusion as the dominant transport mechanism that competes with stochastic roughening. NH3 incident kinetic energies in the 0.4--1.8 eV range did not have a direct effect on surface morphology but an indirect influence via NH3 reactivity modulation. Two-dimensional GaN films were grown by chemical beam epitaxy using TEG-seeded supersonic molecular beams and NH3 from a leak valve. TEM analysis indicated that GaN films were homoepitaxially grown on GaN(0001) substrates but have a high density of planar defects. Substrate temperature was the primary variable in reducing carbon contamination in the films. The dissociative chemisorption pathway of triethylgallium on GaN(0001) also appears to be precursor-mediated.