Evolution of microstructure, stress and dislocation of AlN thick film on nanopatterned sapphire substrates by hydride vapor phase epitaxy

Abstract

A crack-free AlN film with 4.5 μm thickness was grown on a 2-inch hole-type nano-patterned sapphire substrates (NPSSs) by hydride vapor phase epitaxy (HVPE). The coalescence, stress evolution, and dislocation annihilation mechanisms in the AlN layer have been investigated. The large voids located on the pattern region were caused by the undesirable parasitic crystallites grown on the sidewalls of the nano-pattern in the early growth stage. The coalescence of the c-plane AlN was hindered by these three-fold crystallites and the special triangle void appeared. The cross-sectional Raman line scan was used to characterize the change of stress with film thickness, which corresponds to the characteristics of different growth stages of AlN. Threading dislocations (TDs) mainly originate from the boundary between misaligned crystallites and the c-plane AlN and the coalescence of two adjacent c-plane AlN crystals, rather than the interface between sapphire and AlN.