Metalorganic Vapor Phase Epitaxy Growth of <i>a</i> ‐Plane AlGaN and Multiple Quantum Wells on Face‐to‐Face Annealed Sputter‐Deposited AlN/ <i>r</i> ‐Plane Sapphire

AlGaN‐based deep‐ultraviolet light‐emitting diodes (DUV LEDs) are conventionally grown on polar (0001) c ‐plane, which suffers from limited light‐extraction efficiency and reduced internal quantum efficiency (IQE) caused by E // c polarization and the quantum‐confined Stark effect. These issues can potentially be addressed using nonpolar a ‐plane as the growth plane. Our group has fabricated high‐quality a ‐plane AlN on r ‐plane sapphire by the combination of sputtering and face‐to‐face annealing (FFA Sp‐AlN). Herein, metalorganic vapor phase epitaxy growth conditions of AlN on a ‐plane FFA Sp‐AlN are investigated, and AlGaN‐based a ‐plane multiple quantum wells (MQWs) are fabricated. The optimized a ‐plane AlN is achieved by optimizing NH 3 flow rate, growth temperature, and substrate off‐angle, exhibiting a root mean squared roughness of less than 1 nm and (11–20) X‐ray rocking curve full‐width of half maximum of 447 arcsec along the c ‐axis (535 arcsec along the m ‐axis of AlN). DUV light emission emitting at 237 nm with strong E // c polarization is obtained from a ‐plane AlGaN‐based MQWs. Although room‐temperature photoluminescence efficiency reaches 18%, the excitation‐density‐dependent measurements at 4 K indicate that the IQE is less than unity, suggesting that further optimization is necessary.