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Proceedings Paper

Analysis on light extraction property of AlGaN-based flip-chip ultraviolet light-emitting diodes by the use of self-assembled SiO2 microsphere array
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Paper Abstract

Light extraction efficiency (ηextraction) remains as a big challenge for high-efficiency deep-ultraviolet (UV) lightemitting diodes (LEDs) due to the large refractive index contrast at the AlN(sapphire)/air interface. Various surface patterning approaches such as microdome design and patterned sapphire substrates have been proposed to address the low ηextraction issue. Nevertheless, these previously proposed methods all involved additional complicated fabrication steps and the polarization-dependent analysis for these devices has not been investigated experimentally. In this work, we investigate the feasibility of using 700-nm SiO2 microsphere array on 280 nm flip-chip UV LEDs to improve the ηextraction. Angle- and polarization-dependent electroluminescence measurements have been performed to compare the 280 nm LEDs with and without the SiO2 microsphere array. The UV LED with microsphere array showed enhancement for transverse-electric (TE)-polarized light intensities at small angles while decreased intensities at large angles with respect to c-axis, as compared to the device without SiO2 microspheres For instance, up to 7.4% enhancement is observed at θ = 0°. However, for transverse-magnetic (TM)-polarized light, the intensities largely remain the same at small angles while decrease at large angles. Cross-sectional near-field electric field distribution from three-dimensional finite-difference time-domain simulation has confirmed that the use of SiO2 microspheres array resulted in scattering of photons at the sapphire/SiO2 microspheres interface, which eventually leads to enhanced TE-photons extraction at small-angles. From simulation, the light radiation patterns from the UV LED with SiO2 spheres are reshaped to a small-angle-favored pattern without reducing the total output power, showing great consistency with the measurement results.

Paper Details

Date Published: 1 March 2019
PDF: 6 pages
Proc. SPIE 10918, Gallium Nitride Materials and Devices XIV, 109180Q (1 March 2019); doi: 10.1117/12.2510488
Show Author Affiliations
Cheng Liu, Rochester Institute of Technology (United States)
Bryan Melanson, Rochester Institute of Technology (United States)
Yu Kee Ooi, Rochester Institute of Technology (United States)
Matthew Hartensveld, Rochester Institute of Technology (United States)
Jing Zhang, Rochester Institute of Technology (United States)

Published in SPIE Proceedings Vol. 10918:
Gallium Nitride Materials and Devices XIV
Hiroshi Fujioka; Hadis Morkoç; Ulrich T. Schwarz, Editor(s)

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