Plasma assisted molecular beam epitaxial growth of AlGaN films with high AlN molar fraction on AlN templates

Abstract High-quality Aluminum gallium nitride (AlGaN) layers with high aluminum (Al) composition are promising candidates for developing ultraviolet (UV) emitters based on III-nitrides. In this work, 150 nm thick Al x Ga 1-x N epilayers with Al composition ranging from x ~ 0.6 to 0.9 were coherently grown on an AlN template using plasma-assisted molecular beam epitaxy (PA-MBE). The influence of Ga/Al beam flux ratio on the surface morphology and crystalline quality of AlGaN was systematically investigated. It was found that the Al composition could be effectively tuned by adjusting the Al flux under metal-rich growth conditions. Furthermore, increasing the Ga beam flux within an appropriate range promoted Al 0.9 Ga 0.1 N step-flow epitaxial growth, resulting in AlGaN epilayers with clear atomic steps. This improvement is attributed to the surfactant role of Ga, which enhances the migration rate of Al adatoms on the growing surface, thereby improving both the surface morphology and crystalline quality of high-Al-composition AlGaN.