Greatly improved crystal quality of non‐polar GaN grown on a‐plane GaN nano‐rod template obtained using self‐organised nano‐masks

Abstract

AbstractWe have developed a simple and effective approach for growth of a‐plane GaN with massively improved crystal quality on a‐plane GaN nanorod template on sapphire. The a‐plane GaN nanorod template is fabricated using self‐organised nickel nano‐masks. X‐ray diffraction rocking curves, measured along both symmetrical and asymmetrical directions, show a massive reduction in full width at half maximum (FWHM), meaning a significant reduction in dislocation density. These are all among best reports although our overgrown layer is only 4‐5 μm, much less than those using any other overgrowth technique. The threading dislocation density has been reduced down to 2.5×108 cm‐2 from typical 9×109 cm‐2 for the a‐plane GaN template on sapphire. The scanning electron microscope measurements show that two kinds of voids have been observed in the cross‐sectional image, which form during the coalescence process of the overgrowth. Taking the advantage of the SiO2 remaining on the top of the nano‐rods, theoretically all dislocations could be effectively blocked. Photoluminescence (PL) measurements have been performed, showing a strong band‐edge emission, which cannot be observed in the a‐plane GaN template on sapphire (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)