Influence of sapphire substrate miscut on the surface morphology and microstructure of AlN films grown by HVPE

The surface morphology and microstructure of c-plane AlN thick films grown by hydride vapor phase epitaxial (HVPE) have been firstly investigated in dependence on the miscut angle of sapphire substrates and the gas flow of HCl. AlN films grown on substrate with 0.2 degrees miscut show relatively flat surface and the decreased HCl gas flow leads to the surface morphology transition from step-flow to step-bunching. Correspondingly, AlN thick films grown on substrate with 4 degrees miscut at both HCl gas flow of 0.025 sccm and 0.015 sccm show step bunching morphology and the surface is rough. AlN thick films grown on sapphire substrate with 4 degrees miscut have lower dislocation density, which is attributed to the macro-steps on the surface and the narrow atomic steps on substrates. Both macro-steps and narrow atomic steps promote the formation of inclined threading dislocations (TDs), thereby improving the quality of AlN thick films.