This study examined the effects of HT-AlN and LT-GaN buffer layers on the optical properties, crystallinity and morphology of 3D a-plane GaN structures with InGaN/GaN MQWs. The 3D a-plane GaN on the HT-AlN buffer layer showed a rough surface and various facets, whereas the 3D a-plane GaN on the LT-GaN buffer layer contained mainly {1 0 (1) over bar 1} facets that were tilted 25 degrees to the c-axis giving a pyramidal shape. Narrower full-width at half maximum and higher intensity of the cathodoluminescence spectra of 3D a-plane GaN with InGaN/GaN MQWs were observed with the LT-GaN buffer layer. The monochromatic cathodoluminescence images at a specific wavelength showed that the LT-GaN buffer layer can effectively improve the region of 3D a-plane GaN with InGaN/GaN MQWs. (C) 2010 Published by Elsevier B.V.