Growth and characterization of high quality epitaxial GaN on ZnO(0001) by reactive molecular beam epitaxy

High quality wurtzite GaN epilayers have been grown on oxygen and zinc surfaces of ZnO(0001) substrates by reactive molecular beam epitaxy. Optical measurements point to high quality presumably due to the near close match of both the crystal lattice parameter and the stacking order between GaN and ZnO. The optional and structural characterization of the GaN epilayers and ZnO substrates was performed using photoluminescence, reflectivity, atomic force microscopy, and transmission electron microscopy. Although atomic force microscopy results indicate that the zinc face of ZnO is smoother than the oxygen-face, optical measuremets demonstrate that the oxygen face leads to higher quality GaN compared to the zinc-face. The surface roughness has been reduced by using an intermediate low temperature GaN buffer layer. Transmission electron microscopy and electron diffraction pattern show a considerable improvement in crystal quality of the GaN top-region compared to the interface region.