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Increased Light Extraction of Thin-Film Flip-Chip UVB LEDs by Surface Texturing

M.A. Bergmann1, J. Enslin2, M. Guttmann2, L. Sulmoni2, N. Lobo Ploch3, F. Hjort1, T. Kolbe3, T. Wernicke2, M. Kneissl1,3, and A. Haglund1

Published in:

ACS Photonics, vol. 10, no. 2, pp. 368−373, doi:10.1021/acsphotonics.2c01352 (2023).


Ultraviolet light-emitting diodes (LEDs) suffer from a low wall-plug efficiency, which is to a large extent limited by the poor light extraction efficiency (LEE). A thin-film flip-chip (TFFC) design with a roughened N-polar AlGaN surface can substantially improve this. We here demonstrate an enabling technology to realize TFFC LEDs emitting in the UVB range (280−320 nm), which includes standard LED processing in combination with electrochemical etching to remove the substrate. The integration of the electro-chemical etching is achieved by epitaxial sacrificial and etch block layers in combination with encapsulation of the LED. The LEE was enhanced by around 25% when the N-polar AlGaN side of the TFFC LEDs was chemically roughened, reaching an external quantum efficiency of 2.25%. By further optimizing the surface structure, our ray-tracing simulations predict a higher LEE from the TFFC LEDs than flip-chip LEDs and a resulting higher wall-plug efficiency.

1 Chalmers University of Technology, Department of Microtechnology and Nanoscience, 41296  Gothenburg, Sweden
2 Technische Universität Berlin, Institute of Solid State Physics, 10623 Berlin, Germany
3 Ferdinand-Braun-Institut gGmbH, Leibniz-Institut für Höchstfrequenztechnik, 12489 Berlin, Germany


light-emitting diode, AlGaN, ultraviolet, electrochemical etching, surface texturing, light extraction

Copyright © 2023 The Authors. Published by American Chemical Society
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