Control of Metal-Rich Growth for GaN/AlN Superlattice Fabrication on Face-to-Face-Annealed Sputter-Deposited AlN Templates

GaN/AlN superlattices consisting of few-monolayer GaN wells have attracted considerable attention for use in deep-ultraviolet (DUV) light-emitting devices. To avoid the formation of droplets and AlGaN interface layers, precise growth control is essential for fabricating superlattices with flat and abrupt interfaces. Herein, GaN/AlN superlattice structures are grown on face-to-face-annealed sputter-deposited AlN (FFA Sp-AlN) template substrates using radio-frequency plasma-excited molecular beam epitaxy (RF-MBE) utilizing in situ reflection high-energy electron diffraction (RHEED) monitoring. Both AlN and GaN are grown under metal-rich conditions, and subsequently, the droplets are eliminated by droplet elimination by radical beam irradiation (DERI) method for AlN and by growth interruption for GaN. Furthermore, the dependence of AlN thickness on the properties of superlattices is investigated. The AlN thickness changes linearly with the supply time of the Al metal; thus, the AlN thickness is easily controllable. A total of 20-period GaN/AlN superlattices with flat and abrupt interfaces is fabricated, as confirmed using atomic force microscopy and X-ray diffraction. Cathodoluminescence with a peak wavelength of 230-260 nm at room temperature is obtained from the fabricated superlattices. Moreover, the emission wavelength shifts with an increase in AlN thickness.