Growth of thick A1N epilayers with droplet-free and atomically smooth surface by plasma-assisted molecular beam epitaxy using laser reflectometry monitoring

摘要

Low-temperature (< 750 ℃) growth of thick A1N epilayers on c-sapphire by plasma-assisted molecular-beam epitaxy under the Al-rich conditions (F_(Al)/P_N~* < 1.4) is reported here. Short periodic Al-flux interruptions controlled precisely by laser reflectometry ensure continuous growth of droplet-free and atomically smooth A1N films (rms < 2 ML over 4 μm~2) with a growth rate governed by the activated nitrogen flux. Lateral spreading of small accumulated Al clusters with their subsequent incorporation into the A1N layer during the Al-flux interruptions is supposed to be facilitated by activated nitrogen radicals. Strong influence of the remaining Al droplets on the subsequent growth of AlGaN/AIN superlattices is also demonstrated.