[16p-A21-1~14] 15.4 III-V-group nitride crystals

4:45 PM - 5:00 PM JST(7:45 AM - 8:00 AM UTC)English Presentation

[16p-A21-14] Revisiting the Growth Temperature Dependence of n-AlGaN Buffer Layer and Quantum-Well in (228-230 nm)-Band far-UVC LEDs

〇Muhammad Ajmal Khan¹, Mitsuhiro Muta², Kohei Fujimoto^1,3, Yuya Nagata^1,3, Yukio Kashima¹, Eriko Matsuura¹, Sachie Fujikawa³, Hiroyuki Yaguchi³, Yasushi Iwaisako², Hideki Hirayama¹ (1.RIKEN, 2.Nippon Tungsten Co., Ltd. Japan, 3.Saitama University)

Keywords:

far-UVC LED,MOCVD,n-AlGaN Buffer and Quantum-Well

Aluminum gallium nitride-based (228-230 nm)-band far-ultraviolet-C (far-UVC) light sources can safely be used as a germicidal application in both manned as well as in unmanned environments including space station against these MROs including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Influenza, Salmonella, E. Coli, bedbugs, mold and other germs. Previously, the far-UVC LED with emission power of 1.8 mW and the external quantum efficiency (EQE) of 0.32% at peak wavelength of 228 nm on wafer was reported, however the n-AlGaN buffer layer (BL) was not optimized in the context of relaxation ratio. Because the low relaxation ratio underneath the multi quantium-well (MQWs) is critical for the suppression of transvers magnetic (TM)-mode as well as for promoting the transverse electric (TE)-mode emission (along c-axis). Previously, the influence of growth temperature on MQWs in the context of I-V characteristic was not studied. Herein, the growth temperature dependent relaxation ratio and variation of Al-composition in the n-AlGaN BL and electrical properties of (228 - 230 nm)-band far-UVC LED grown on c-Sapphire are investigated. As a result the relaxation ratio in the n-AlGaN BL was successfully reduced from 41.6% to 20%, and the Al-composition was also varied from 85% to 87%. Quite high electron concentration as well as low resistivity in n-AlGaN electron injection layer (EIL) was realized. As a result, the light power and EQE were significantly improved to 2.4 mW and 0.40% under pulse-operation and to 1.75 mW and 0.35% under CW-operation (RT) at emission wavelength of 230 nm on bar-wafer. The operating voltage was also reduced from 28 V to 24 V in 230 nm far-UVC LED. We also found that the growth of n-AlGaN BL at 1060-1180℃ is advantageous in term of electrical properties but not good option for the optical light polarization (TE-mode and TM-mode).