Thick AlN layers grown on micro-scale patterned sapphire substrates with sputter-deposited annealed AlN films by hydride vapor-phase epitaxy

Misaligned crystallite growth is found on the sidewalls of dome-shaped patterns which hinders the coalescence of the c-plane AlN layer growing on the c-axis-oriented sapphire plane. In this study, thick AlN layers without cracks were grown by hydride vapor-phase epitaxy on micro-scale patterned sapphire substrates using annealed sputter-deposited AlN with a thickness of 200 nm. It was observed that undesired misaligned AlN growth can be prevented by selecting an appropriate growth temperature. A two-step approach was used to promote the lateral growth and coalescence of AlN. A relatively smooth surface without discontinuities and holes was obtained. The influence of the multi-oriented sapphire facets provided by micro-scale patterned sapphire substrates was investigated. According to the geometry of the misaligned crystallites, the grown AlN deviating from the c-axis on the near sapphire r-plane sidewalls has less influence on the coalescence of AlN, compared to the near n-plane sidewalls.