Elimination of Crystallographic Wing Tilt of Canti-BridgedEpitaxial Laterally Overgrown GaN Films by Optimizing Growth Procedure

Abstract

Canti-bridged epitaxial lateral overgrowth (CBELO) of GaN is performedby metalorganic chemical vapour deposition (MOCVD) on maskless V-groovedsapphire substrates prepared by wet chemical etching with different mesawidths. The wing tilt usually observed in ELO is not found in the CBELOGaN with wide mesa widths, while it can be detected obviously in the GaNwith narrow mesa widths. The wing tilt of CBELO GaN grown on a groovedsapphire substrate with narrow mesa can be controlled by adjusting thethickness of the nucleation layer. The dependence of the wing tilt onthe nucleation layer thickness is studied. Cross-sectional scanningelectron microscopy is used to characterize the geometry of the wingregions, and double crystal x-ray diffraction is used to analyse thestructural characteristics and to measure the magnitude of thecrystalline wing tilt. It is found that the crystalline wing tilt can beeliminated completely by first growth of a thin nucleation GaN layerthen the CBELO GaN. Possible reason and the origin of the wing tilt inCBELO GaN films are also discussed.