The crystal quality of a-plane GaN films was improved by using epitaxial lateral overgrowth on trenched a-plane GaN buffer layers. Not only the threading dislocation density but also the difference of anisotropic in-plane strain between orthogonal crystal axes could be mitigated by using trenched epitaxial lateral overgrowth. The low threading dislocation density investigated by cross-sectional transmission electron microscopy was estimated to be 3 x 107/cm2 on the N-face GaN wing. On the other hand, the Ga-face GaN wing, with a faster lateral overgrowth rate, could be influenced by the thin GaN layer grown on the bottom of the trenches, resulting in a higher generated dislocation density. As a result, it was concluded that narrower stripped GaN seeds and deeper stripped trenches, etched into the surface of sapphire, could produce a better-quality a-plane GaN film. A fast coalescence process was demonstrated for trenched epitaxial lateral overgrown GaN films which were less than 10µm thick.

Trenched Epitaxial Lateral Overgrowth of Fast Coalesced a-Plane GaN with Low Dislocation Density. T.C.Wang, T.C.Lu, T.S.Ko, H.C.Kuo, M.Yu, S.C.Wang, C.C.Chuo, Z.H.Lee, H.G.Chen: Applied Physics Letters, 2006, 89[25], 251109 (3pp)