Dislocation reduction mechanisms in gallium nitride films grown by canti-bridge epitaxy method

摘要

By using the special maskless V-grooved c-plane sapphire as the substrate,we previously developed a novel GaN LEO method, or the so-called canti-bridge epitaxy (CBE), and consequently wing-tilt-free GaN films were obtained with low dislocation densities, with which all the conventional difficulties can be overcome [J. Vacuum Sci. Technol. B 23 (2005) 2476]. Here the evolution manner of dislocations in the CBE GaN films is investigated using transmission electron microscopy. The mechanisms of dislocations reduction are discussed. Dislocation behaviour is found to be similar to that in the conventional LEO GaN films except the enhanced dislocation-combination at the coalescence boundary that is a major dislocation-reduction mechanism for the bent horizontal-propagating dislocations in the CBE GaN films. The enhancement of this dislocation-combination probability is believed to result from the inclined shape and the undulate morphology of the sidewalls,which can be readily obtained in a wide range of applicable film-growth conditions during the GaN CBE process. Further development of GaN CBE method and better crystal-quality of the GaN film both are expected.