Enhanced light extraction efficiency of far-ultraviolet-C LEDs by micro-LED array design

• Published in: Applied physics letters Vol. 122; no. 26
• Main Authors: Rass, Jens, Cho, Hyun Kyong, Guttmann, Martin, Prasai, Deepak, Ruschel, Jan, Kolbe, Tim, Einfeldt, Sven
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 26-06-2023
• Subjects: Applied physics; Arrays; Emitters; Light emitting diodes; Polarized light; Quantum efficiency; Quantum wells; Sapphire; Silicon dioxide
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/5.0154031

AlGaN-based far-UVC light emitting diodes (LEDs) with an emission wavelength of 233 nm were fabricated in the form of micro-LED arrays with emitter diameters ranging from 1.5 to 50 μm. The mesa was plasma etched with a sidewall angle of 45°–50°, and insulator layers made of SiNx or SiO2 were deposited. While the external quantum efficiency (EQE) of the LEDs with SiNx showed only a small dependency on the micro-LED diameter, the LEDs using SiO2 showed an increase in the peak EQE by a factor of four as compared to large area devices. This enhancement is attributed to a strong increase in the light extraction efficiency due to total internal reflection and re-direction at the inclined mesa, allowing TM-polarized light emitted in the plane of the quantum well to be extracted through the sapphire backside of the chips.