High-quality AlN grown on a thermally decomposed sapphire surface

Abstract

In this study we show how to realize a self-assembled nano-patterned sapphire surface on 2inch diameter epi-ready wafer and the subsequent AlN overgrowth both in the same metal-organic vapor phase epitaxial process. For this purpose in-situ annealing in H2 environment was applied prior to AlN growth to thermally decompose the c-plane oriented sapphire surface. By proper AlN overgrowth management misoriented grains that start to grow on non c-plane oriented facets of the roughened sapphire surface could be overcome. We achieved crack-free, atomically flat AlN layers of 3.5µm thickness. The layers show excellent material quality homogeneously over the whole wafer as proved by the full width at half maximum of X-ray measured ω-rocking curves of 120arcsec to 160arcsec for the 002 reflection and 440arcsec to 550arcsec for the 302 reflection. The threading dislocation density is 2∗109cm−2 which shows that the annealing and overgrowth process investigated in this work leads to cost-efficient AlN templates for UV LED devices.