Effects and mechanisms of In surfactant on high Al-content AlGaN grown by plasma-assisted molecular beam epitaxy.

ABSTRACT

High Al-content AlGaN epilayers were grown on AlN template by using indium (In) surfactant with plasma-assisted molecular beam epitaxy (PA-MBE), and deep ultraviolet emission at 235 nm was obtained at room temperature. The effects and mechanisms of In-surfactant on the crystalline quality and optical properties of AlGaN were investigated. It was found that In-surfactant could facilitate two-dimensional AlGaN growth by reducing activation barrier for Al/Ga atoms to cross steps and effectively increasing the migration rate on the growth surface, and thus improve surface morphology and decrease defect density. The photoluminescence measurements revealed that the optical properties were remarkably improved by adopting In as surfactant, and phase separation was also effectively eliminated. Furthermore, the concentration of impurities including oxygen and silicon was decreased, which is attributed to higher defects formation energy for these impurities with In-surfactant assisted epitaxy growth.