Investigation of nanopatterned c-plane sapphire Substrates for Growths of polar and nonpolar GaN epilayers

The nanopatterned c -plane sapphire substrate with different morphologies can be successfully used to grow polar and nonpolar GaN epilayers. The nanopattern of sapphire substrate was prepared with natural lithography and dry-etching methods and the following GaN epilayer was grown by MOCVD. The GaN crystal orientation and crystalline quality were then characterized by high resolution X-ray diffraction, which reveals the GaN epilayer can be c -plane (0001) or m -plane (1010) orientation depending on the surface morphology of nanopatterned sapphire substrate. The corresponding full width at half maximum of the rocking curves for c - and m -plane GaN are 211 and 316 arcsec, respectively. The rms surface roughness was measured to be 0.3 nm by atomic force microscopy. The atomic structure of the sapphire-GaN heterointerface was studied by high resolution transmission electron microscope to reveal the growth mechanism. Furthermore, photoluminescence, time-resolved photoluminescence, and polarization Raman spectroscopy were employed to realize the optical and structural properties of these GaN epilayers.