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Photonic crystal based control of directionality in GaN based LEDs

Photonic crystal based control of directionality in GaN based LEDs
Photonic crystal based control of directionality in GaN based LEDs

LED surface structuring has been widely used to increase light extraction[1]. Due to the high refractive index of the thick GaN epitaxy layers, most emitted light becomes trapped and reabsorbed by the epitaxial layers. While random structuring can effectively scatter trapped light out of the LED, it gives little control over the resulting beam-shapef[2]. Photonic crystals however provide a means to simultaneously improve light extraction efficiency and control beam directionality. Furthermore, P-side up LEDs normally utilize a transparent top contact layer in order to allow top light emission whilst maintaining good electrical properties. In this paper we investigate a novel photonic crystal LED configuration with a nontransparent metal top contact layer, and cylindrical holes etched through the top contact layer and deep into the underlying epitaxy. In this novel configuration light emission is only possible from the etched holes giving rise to extreme beam steering effects. We utilize broadband spectroscopic reflectometry to experimentally investigate beam shape and optical properties from fabricated devices. We observe a range of achievable beam patterns with extreme deviations from the normal Lambertian. We investigate the effect of square and triangular photonic crystal lattices on beam directionality.

Directionality, GaN, LEDs, Photonic Crystals
0277-786X
SPIE
Mercier, Thomas M.
48bf8bb9-2952-41f6-8153-354763a06edd
Krishnan, Chirenjeevi
0d41ebc9-118a-4f89-889e-8ad28a69237e
Shaw, Peter J.
dcb6c9af-bf38-4dfe-8395-8aeac2ad5cc7
Lagoudakis, Pavlos G.
ea50c228-f006-4edf-8459-60015d961bbf
Charlton, Martin D.B.
fcf86ab0-8f34-411a-b576-4f684e51e274
Kim, Jong Kyu
Krames, Michael R.
Strassburg, Martin
Mercier, Thomas M.
48bf8bb9-2952-41f6-8153-354763a06edd
Krishnan, Chirenjeevi
0d41ebc9-118a-4f89-889e-8ad28a69237e
Shaw, Peter J.
dcb6c9af-bf38-4dfe-8395-8aeac2ad5cc7
Lagoudakis, Pavlos G.
ea50c228-f006-4edf-8459-60015d961bbf
Charlton, Martin D.B.
fcf86ab0-8f34-411a-b576-4f684e51e274
Kim, Jong Kyu
Krames, Michael R.
Strassburg, Martin

Mercier, Thomas M., Krishnan, Chirenjeevi, Shaw, Peter J., Lagoudakis, Pavlos G. and Charlton, Martin D.B. (2020) Photonic crystal based control of directionality in GaN based LEDs. Kim, Jong Kyu, Krames, Michael R. and Strassburg, Martin (eds.) In Light-Emitting Devices, Materials, and Applications XXIV. vol. 11302, SPIE.. (doi:10.1117/12.2543124).

Record type: Conference or Workshop Item (Paper)

Abstract

LED surface structuring has been widely used to increase light extraction[1]. Due to the high refractive index of the thick GaN epitaxy layers, most emitted light becomes trapped and reabsorbed by the epitaxial layers. While random structuring can effectively scatter trapped light out of the LED, it gives little control over the resulting beam-shapef[2]. Photonic crystals however provide a means to simultaneously improve light extraction efficiency and control beam directionality. Furthermore, P-side up LEDs normally utilize a transparent top contact layer in order to allow top light emission whilst maintaining good electrical properties. In this paper we investigate a novel photonic crystal LED configuration with a nontransparent metal top contact layer, and cylindrical holes etched through the top contact layer and deep into the underlying epitaxy. In this novel configuration light emission is only possible from the etched holes giving rise to extreme beam steering effects. We utilize broadband spectroscopic reflectometry to experimentally investigate beam shape and optical properties from fabricated devices. We observe a range of achievable beam patterns with extreme deviations from the normal Lambertian. We investigate the effect of square and triangular photonic crystal lattices on beam directionality.

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More information

Published date: 25 February 2020
Venue - Dates: Light-Emitting Devices, Materials, and Applications XXIV 2020, , San Francisco, United States, 2020-02-03 - 2020-02-06
Keywords: Directionality, GaN, LEDs, Photonic Crystals

Identifiers

Local EPrints ID: 445612
URI: http://eprints.soton.ac.uk/id/eprint/445612
ISSN: 0277-786X
PURE UUID: e134af00-0596-40d0-b396-e2da139e124a
ORCID for Peter J. Shaw: ORCID iD orcid.org/0000-0001-9044-1069

Catalogue record

Date deposited: 18 Dec 2020 17:30
Last modified: 18 Dec 2020 17:30

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Contributors

Author: Thomas M. Mercier
Author: Chirenjeevi Krishnan
Author: Peter J. Shaw ORCID iD
Author: Martin D.B. Charlton
Editor: Jong Kyu Kim
Editor: Michael R. Krames
Editor: Martin Strassburg

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