AlN growth on nano-patterned sapphire: A route for cost efficient pseudo substrates for deep UV LEDs

Abstract

C-plane-oriented sapphire substrates that were patterned on the nanoscale were overgrown by AlN using metal-organic vapor phase epitaxy. The occurrence of undesired misaligned AlN growth was detected. We found that this misaligned growth can be overcome by a proper choice of growth temperature and V/III ratio. Up to 8 μm thick c-plane-oriented AlN with a coalesced surface was obtained. An effective dislocation reduction was found due to bending of threading dislocation lines toward free surfaces during lateral growth. The distribution of crystal defects suggests that step bunching in AlN is accompanied by dislocation accumulation. Furthermore, nearly defect-free AlN crystallites with a hexagonal shape and a size of about 2 μm were observed. Schematic cross-section representation of AlN grown on nano-patterned sapphire. Different AlN crystal orientations (arrows) and dislocations (solid black lines) are indicated.