10.1021/acs.nanolett.6b00892.s001
Yoon-Jong Moon
Yoon-Jong
Moon
Daeyoung Moon
Daeyoung
Moon
Jeonghwan Jang
Jeonghwan
Jang
Jin-Young Na
Jin-Young
Na
Jung-Hwan Song
Jung-Hwan
Song
Min-Kyo Seo
Min-Kyo
Seo
Sunghee Kim
Sunghee
Kim
Dukkyu Bae
Dukkyu
Bae
Eun Hyun Park
Eun Hyun
Park
Yongjo Park
Yongjo
Park
Sun-Kyung Kim
Sun-Kyung
Kim
Euijoon Yoon
Euijoon
Yoon
Microstructured Air Cavities as High-Index Contrast
Substrates with Strong Diffraction for Light-Emitting Diodes
American Chemical Society
2016
air cavity volume
extraction efficiency
CES LEDs
Microstructured Air Cavities
pattern
2016-04-05 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Microstructured_Air_Cavities_as_High_Index_Contrast_Substrates_with_Strong_Diffraction_for_Light_Emitting_Diodes/3160435
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<sup>2</sup>) 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.