Aluminum monolayers on Si (1 1 1) for MBE-growth of GaN

Up to 10 monolayers of Al were deposited on Si (1 1 1) surfaces at low (450 °C) and high (640 °C) temperatures before the molecular beam epitaxy growth of GaN. The influence of the Al monolayers on the overall GaN epitaxial layers was investigated by reflection high-energy electron diffraction, atomic force microscopy, high-resolution X-ray diffraction and transmission electron microscopy. At high-temperature deposition, ∼1.3 monolayer Al gave the smoothest GaN surface and best crystalline quality. At the low temperature, only ∼0.8 ML provided the same GaN quality.