An elegant route to overcome fundamentally-limited light extraction in AlGaN deep-ultraviolet light-emitting diodes: preferential outcoupling of strong in-plane emission (Conference Presentation)

Jong Kyu Kim; Jong Won Lee; Dong-Yeong Kim; Jun Hyuk Park; E. Fred Schubert; Jungsub Kim; Yong-Il Kim

doi:10.1117/12.2236420

11 November 2016 An elegant route to overcome fundamentally-limited light extraction in AlGaN deep-ultraviolet light-emitting diodes: preferential outcoupling of strong in-plane emission (Conference Presentation)

Jong Kyu Kim, Jong Won Lee, Dong-Yeong Kim, Jun Hyuk Park, E. Fred Schubert, Jungsub Kim, Yong-Il Kim

Author Affiliations +

Proceedings Volume 9926, UV and Higher Energy Photonics: From Materials to Applications; 99260F (2016) https://doi.org/10.1117/12.2236420
Event: SPIE Nanoscience + Engineering, 2016, San Diego, California, United States

Abstract

AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) are being developed for their numerous applications such as purification of air and water, sterilization in food processing, UV curing, medical-, and defense-related light sources. However, external quantum efficiency (EQE) of AlGaN-based DUV LEDs is very poor (<5% for 250nm) particularly due to low hole concentration and light extraction efficiency (LEE). Conventional LEE-enhancing techniques used for GaInN-based visible LEDs turned out to be ineffective for DUV LEDs due to difference in intrinsic material property between GaInN and AlGaN (Al<~30%). Unlike GaInN visible LEDs, DUV light from a high Al-content AlGaN active region is strongly transverse-magnetic (TM) polarized, that is, the electric field vector is parallel to the (0001) c-axis and shows strong sidewall emission through m- or a-plane due to crystal-field split-off hole band being top most valence band. Therefore, a new LEE-enhancing approach addressing the unique intrinsic property of AlGaN DUV LEDs is strongly desired. In this study, an elegant approach based on a DUV LED having multiple mesa stripes whose inclined sidewalls are covered by a MgF2/Al omni-directional mirror to take advantage of the strongly anisotropic transverse-magnetic polarized emission pattern of AlGaN quantum wells is presented. The sidewall-emission-enhanced DUV LED breaks through the fundamental limitations caused by the intrinsic properties of AlGaN, thus shows a remarkable improvement in light extraction as well as operating voltage simultaneously. Furthermore, an analytic model is developed to understand and precisely estimate the extraction of DUV photons from AlGaN DUV LEDs, and hence to provide promising routes to maximize the power conversion efficiency.

Conference Presentation

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Jong Kyu Kim, Jong Won Lee, Dong-Yeong Kim, Jun Hyuk Park, E. Fred Schubert, Jungsub Kim, and Yong-Il Kim "An elegant route to overcome fundamentally-limited light extraction in AlGaN deep-ultraviolet light-emitting diodes: preferential outcoupling of strong in-plane emission (Conference Presentation)", Proc. SPIE 9926, UV and Higher Energy Photonics: From Materials to Applications, 99260F (11 November 2016); https://doi.org/10.1117/12.2236420

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KEYWORDS

Deep ultraviolet

Light emitting diodes

External quantum efficiency

Ultraviolet radiation

Crystals

Light sources

Mirrors

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