Strain-free ultrathin AlN epilayers grown directly on sapphire by high-temperature molecular beam epitaxy

High-quality AlN ultrathin films on sapphire substrate were grown by molecular beam epitaxy using an in situ high-temperature annealing approach. From transmission electron microscopy studies, it was found that the AlN epilayers are strain relaxed within the first nm, thus growing nearly strain free. Many of the dislocations generated at the AlN/sapphire interface are reduced within the first 50 nm of growth. Epitaxial films grown directly on …