Epitaxial growth of 2 inch diameter homogeneous AlN single-crystalline films by pulsed laser deposition

2?inch diameter homogeneous AlN films are epitaxially grown on sapphire substrates by pulsed laser deposition (PLD). By optimizing laser rastering and PLD growth conditions, the 2?inch diameter single-crystalline AlN films exhibit excellent thickness uniformity with root-mean-square (RMS) inhomogeneity less than 4.5% and very smooth surface with RMS roughness less than 1.53?nm. There is a maximum of 1.5?nm thick interfacial layer, if there is any, existing between the as-grown AlN and the pre-nitrided sapphire substrate, and the as-grown AlN films are almost fully relaxed only with a 0.26% in-plane compressive strain. The achievement of high-quality large-scale AlN films with uniform thickness and atomically abrupt interface is of great interest for the commercial development of AlN-based devices, particularly acoustic filters where abrupt heterointerfaces with substrates and flat surfaces for AlN films are highly desired.