title: Microstructured Air Cavities as High-Index Contrast Substrates with Strong Diffraction for Light-Emitting Diodes.
abstract: Two-dimensional high-index-contrast dielectric gratings exhibit unconventional transmission and reflection due to their morphologies. For light-emitting devices, these characteristics help guided modes defeat total internal reflections, thereby enhancing the outcoupling efficiency into an ambient medium. However, the outcoupling ability is typically impeded by the limited index contrast given by pattern media. Here, we report strong-diffraction, high-index-contrast cavity engineered substrates (CESs) in which hexagonally arranged hemispherical air cavities are covered with a 80 nm thick crystallized alumina shell. Wavelength-resolved diffraction measurements and Fourier analysis on GaN-grown CESs reveal that the high-index-contrast air/alumina core/shell patterns lead to dramatic excitation of the low-order diffraction modes. Large-area (1075 × 750 μm(2)) blue-emitting InGaN/GaN light-emitting diodes (LEDs) fabricated on a 3 μm pitch CES exhibit ∼39% enhancement in the optical power compared to state-of-the-art, patterned-sapphire-substrate LEDs, while preserving all of the electrical metrics that are relevant to LED devices. Full-vectorial simulations quantitatively demonstrate the enhanced optical power of CES LEDs and show a progressive increase in the extraction efficiency as the air cavity volume is expanded. This trend in light extraction is observed for both lateral- and flip-chip-geometry LEDs. Measurements of far-field profiles indicate a substantial beaming effect for CES LEDs, despite their few-micron-pitch pattern. Near-to-far-field transformation simulations and polarization analysis demonstrate that the improved extraction efficiency of CES LEDs is ascribed to the increase in emissions via the top escape route and to the extraction of transverse-magnetic polarized light.
authors.affiliation: Department of Applied Physics, Kyung Hee University , Gyeonggi-do 17104, Republic of Korea.
authors.forename: Yoon-Jong
authors.initials: YJ
authors.lastname: Moon
authors.affiliation: Department of Materials Science and Engineering, Seoul National University , Seoul 08826, Republic of Korea.
authors.forename: Daeyoung
authors.initials: D
authors.lastname: Moon
authors.affiliation: Department of Materials Science and Engineering, Seoul National University , Seoul 08826, Republic of Korea.
authors.forename: Jeonghwan
authors.initials: J
authors.lastname: Jang
authors.affiliation: Department of Applied Physics, Kyung Hee University , Gyeonggi-do 17104, Republic of Korea.
authors.forename: Jin-Young
authors.initials: JY
authors.lastname: Na
authors.affiliation: Department of Physics, KAIST , Daejeon 34141, Republic of Korea.
authors.forename: Jung-Hwan
authors.initials: JH
authors.lastname: Song
authors.affiliation: Department of Physics, KAIST , Daejeon 34141, Republic of Korea.
authors.forename: Min-Kyo
authors.initials: MK
authors.lastname: Seo
authors.affiliation: Hexa Solution Co., Ltd. , Gyeonggi-do 16229, Republic of Korea.
authors.forename: Sunghee
authors.initials: S
authors.lastname: Kim
authors.affiliation: Hexa Solution Co., Ltd. , Gyeonggi-do 16229, Republic of Korea.|Energy Semiconductor Research Center, Advanced Institutes of Convergence Technology, Seoul National University , Gyeonggi-do 16229, Republic of Korea.
authors.forename: Dukkyu
authors.initials: D
authors.lastname: Bae
authors.affiliation: Semicon Light Co., Ltd. , Gyeonggi-do 17086, Republic of Korea.
authors.forename: Eun Hyun
authors.initials: EH
authors.lastname: Park
authors.affiliation: Department of Materials Science and Engineering, Seoul National University , Seoul 08826, Republic of Korea.|Energy Semiconductor Research Center, Advanced Institutes of Convergence Technology, Seoul National University , Gyeonggi-do 16229, Republic of Korea.
authors.forename: Yongjo
authors.initials: Y
authors.lastname: Park
authors.affiliation: Department of Applied Physics, Kyung Hee University , Gyeonggi-do 17104, Republic of Korea.
authors.forename: Sun-Kyung
authors.initials: SK
authors.lastname: Kim
authors.affiliation: Department of Materials Science and Engineering, Seoul National University , Seoul 08826, Republic of Korea.|Energy Semiconductor Research Center, Advanced Institutes of Convergence Technology, Seoul National University , Gyeonggi-do 16229, Republic of Korea.
authors.forename: Euijoon
authors.initials: E
authors.lastname: Yoon
keywords: FDTD simulation; III-nitride compounds; Light-emitting diodes; high-index-contrast gratings; hollow cavities