“…Previously, the influence of ∼ 50% relaxed n-type AlGaN ESL in 310 nm-band MQWs on PL intensity was reported 8 . However, the influence of ∼ 49% relaxed n-type AlGaN ESL in 304 nm-band MQWs on PL intensity is rarely reported in our previous work 8 , 25 , 26 . The relaxation condition in the n-AlGaN ESL underneath the MQWs, strongly influences the piezoelectricity, extended defects, point defects, Al-alloy fluctuation and nonradiative recombination centers (NRCs) in the MQWs, which ultimately degrade the IQE 4 , 8 , 16 , 26 , 37 , 38 .…”