Effect of flow–substrate angle on the growth quality of AlN films in a horizontal MNVPE reactor

The growth of high-quality AlN films by Metal Nitride Vapor Phase Epitaxy (MNVPE) is often limited by non-uniform reactant distribution and unstable flow fields near the substrate surface. In this work, we find that different angle between the gas flow and the substrate surface can effectively influence both the crystalline quality and surface morphology of thick AlN films grown on sapphire. Computational fluid dynamics (CFD) simulations confirmed that the small-angle conicaler substrate holder improves the premixing uniformity of Al vapor and N₂, while stabilizing the gas flow above the substrate. Experimental results show that, compared to the large-angle case, the full width at half maximum (FWHM) of the (0002) and (101 ̅2) X-ray rocking curves was significantly reduced from 849 to 458 arcsec and from 935 to 565 arcsec, respectively. The surface roughness (RMS) reached 2.65 nm, and the growth rate increased from 5 to 15 μm/h. Growth evolution analysis revealed a c-axis-oriented island coalescence mechanism. These results demonstrate that adjusting the flow–substrate angle is a simple yet effective approach to significantly enhance the MNVPE growth of AlN films.Key words: MNVPE AlN Single crystal growth.