Light extraction analysis of AlGaN nanowires with inverse taper for DUV LEDs

Bryan Melanson; Cheng Liu; Matthew Hartensveld; Jing Zhang

doi:10.1117/12.2583116

5 March 2021 Light extraction analysis of AlGaN nanowires with inverse taper for DUV LEDs

Bryan Melanson, Cheng Liu, Matthew Hartensveld, Jing Zhang

Proceedings Volume 11706, Light-Emitting Devices, Materials, and Applications XXV; 117060I (2021) https://doi.org/10.1117/12.2583116
Event: SPIE OPTO, 2021, Online Only

Abstract

Planar deep-ultraviolet (DUV) light emitting diodes (LEDs) suffer from extremely low external quantum efficiencies (EQEs) due to poor light extraction efficiencies (LEE) which are often less than 1%, hindering their widespread use. In AlGaN DUV LEDs with high Al-content, the positioning of the valence subbands leads to dominant transverse magnetic (TM)-polarized emission which is difficult to extract from planar devices. To improve the LEE of DUV LEDs, techniques such as surface roughening and nanowire formation have been used. Nanowires are especially promising for DUV LEDs because they allow for very efficient extraction of TM-polarized light through their sidewalls. In this work, we demonstrate a novel “inverse taper” profile in AlGaN nanowires, in which the base of the nanowire can be narrowed to have a smaller diameter than the top through a KOH-based wet etch process. Hydroxyl-based chemistries are known to have a lower etch rate against the c-plane of wurtzite AlGaN alloys. Here, we report on observations of 0.8% KOH at 80℃ exhibiting a unique selectivity to a different wurtzite crystal plane, believed to be the (202̅ 1) plane, allowing for formation of an inverse taper structure. Finite difference time domain (FDTD) simulations at 280 nm reveal that AlGaN nanowire LEDs with high sidewall inverse taper angles can have greater than 75% and 90% LEE for TE and TM-polarized light respectively, ~2.5x higher than the LEE of vertical sidewall nanowires. This novel phenomenon may allow for significant improvements in the LEE of DUV nanowire LEDs.

Conference Presentation

Citation Download Citation

Bryan Melanson, Cheng Liu, Matthew Hartensveld, and Jing Zhang "Light extraction analysis of AlGaN nanowires with inverse taper for DUV LEDs", Proc. SPIE 11706, Light-Emitting Devices, Materials, and Applications XXV, 117060I (5 March 2021); https://doi.org/10.1117/12.2583116

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