Gas-source molecular beam epitaxy, employing Ga and NH3, and reactive-ion molecular beam epitaxy, involving thermal NH3 and low-energy NHx+ ions, were used to grow monocrystalline (00•1) GaN layers onto (00•1) Al2O3 at temperatures of between 700 and 850C; at deposition rates of 0.2 to 0.5/h. The reactive-ion molecular beam epitaxy experiments were performed using incident NHx+/Ga flux ratios of between 1.9 and 3.2, and NHx+ acceleration energies of 45 to 90eV. Plan-view and cross-sectional transmission electron microscopic studies showed that the main defects in the gas-source molecular beam epitaxial films were threading dislocations which had either pure edge or mixed edge/screw characteristics with Burgers vectors of 1/3<2¯1•0>, basal-plane stacking faults with displacement vectors of 1/6<02•3>, and prismatic stacking faults with a displacement vector of 1/2<¯11•1>. In the case of reactive-ion molecular beam epitaxial films, no stacking faults or residual ion-induced defects were observed for an NHx+ acceleration energy of 45eV at temperatures above 800C. However, increasing the NHx+ acceleration energy to more than 60eV at 800C gave rise to the formation of residual ion-induced point-defect clusters; as observed using transmission electron microscopy. Increasing the temperature to 850C, for NHx+ acceleration energies of more than 60eV, resulted in the aggregation of ion-induced defects to form interstitial basal and prismatic dislocation loops (whose number densities depended upon the ion flux) with Burgers vectors of 1/2<00•1> and 1/3<2¯1•0>, respectively.

N.E.Lee, R.C.Powell, Y.W.Kim, J.E.Greene: Journal of Vacuum Science and Technology A, 1995, 13[5], 2293-302