Selective growth and characterization of GaN nanowires on SiC substrates

Abstract

GaN on SiC is a promising material combination for high power devices, where especially nanostructures, such as nanowires or nanofins, are a space and resource saving solution. In this work we demonstrate the selective area growth of GaN nanowires on SiC substrates, using the polytype 6H-SiC. We investigate the influence of the Si- and C-polarity of the substrate on the structural properties of the GaN nanowires by scanning electron microscopy and photoluminescence spectroscopy. On both substrates uniform and hexagonal nanowires are achieved for the respective optimal growth temperature, which is determined to be 20 ^{$\circ $}C higher for Si-polarity. As the polarity combination of the SiC substrate and GaN nanowires strongly influences the electrical properties at the heterointerface due to different charge accumulations, it is necessary to investigate the epitaxial relationship. X-ray diffraction revealed that the GaN nanowires exclusively adopt the orientation of the underlying SiC lattice, leading to an in-plane epitaxial relationship of (1$\overline{1}$00)GaN/(1$\overline{1}$00)6H-SiC. Polarity-selective wet chemical etching and Kelvin probe force microscopy showed that the GaN nanowires preserve the polarity of the substrate, thus, either a predominantly metal-polar (Si-polar/Ga-polar) or non-metal-polar (C-polar/N-polar) orientation is present. The complete epitaxial relationship on both substrate polarities can be identified as (1$\overline{1}$00)[0001]GaN$\left|\right|$(1$\overline{1}$00)[0001]6H-SiC for the large majority of NWs at their respective optimum growth temperatures.