High-Quality Growth of AlN Epitaxial Layer by Plasma-Assisted Molecular-Beam Epitaxy

We report the growth and characterization of high-quality h-AlN epitaxial layers on basal c -plane sapphire substrates by plasma-assisted molecular-beam epitaxy (MBE). The c -axis lattice constant has been found to vary with the layer thickness. AlN layers grown in an intermediate Al/N growth regime show a 2D streaky reflection high-energy electron diffraction (RHEED) pattern and the surface morphologies have few surface irregularities, and sufficient to speculate that the layers are free from large Al metal droplets. The full width at half maximum (FWHM) (ω scan) of the AlN layers along the symmetric (0002) and asymmetric (11–24) diffraction planes were 42 and 180 arcsec, respectively. Excitonic transitions ( D °, X and A °, X ), indicating high quality of the layers, have been found in all the samples by cathodoluminescence measurements, and a violet band has been attributed to either shallow or deep donor pair recombination.