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Keywords:

  • a-plane GaN;
  • nanorod overgrowth;
  • crystal quality

Abstract

We 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)