High extraction efficiency light-emitting diodes based on embedded air-gap photonic-crystals

Matioli, Elison; Rangel, Elizabeth; Iza, M.; Fleury, Blaise; Pfaff, Nathan; Speck, James S.; Hu, Evelyn L.; Weisbuch, C.

doi:10.1063/1.3293442

Cited by 97 publications

(70 citation statements)

References 14 publications

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“…This can be achieved by several different configurations of PhCs, such as deeper surface PhCs ͑ϳ150-200-nm-deep͒, thin-film LEDs with surface PhCs, 10 or embedded PhCs. 19,20 The present technique can be extended to experimentally determine losses by metallic layers from electrical contacts or other dissipation mechanisms in optoelectronic devices.…”

Section: Discussionmentioning

confidence: 99%

Measurement of extraction and absorption parameters in GaN-based photonic-crystal light-emitting diodes

Matioli

Fleury

Rangel

et al. 2010

Journal of Applied Physics

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The light extraction efficiency of photonic-crystal ͑PhC͒ light-emitting diodes ͑LEDs͒ relies on the competition between the PhC extraction and dissipation mechanisms of the guided light within the LED. This work presents the experimental determination of the PhC extraction length of each guided mode and the absorption coefficient of the active region ͑AR͒ and quantum wells ͑QWs͒ from the observation of the LED far-field emission using a high-resolution angle-spectrum-resolved measurement. The angular and spectral linewidths of the extracted guided modes reveal, depending on the spectral range, the modal extraction length of the PhCs, the AR absorption length, or a combination of both. Modes with a high confinement with the QWs presented a shorter absorption length compared with their extraction length by a shallow surface PhC ͑95-nm-deep͒, meaning that the AR absorption was a more efficient mechanism than the PhC extraction. The measured modal extraction length of the shallow surface PhC varied in the range of 55-120 m, which determines the minimum dimensions of the device and the maximum acceptable dissipation length for an efficient extraction of the guided light by the PhCs. This paper presents also a discussion on the PhC designs that yield PhC extraction lengths shorter than other dissipation lengths, a fundamental requirement for high-efficiency PhC LEDs. The same technique was also applied to estimate the absorption coefficient of the InGaN-based QWs, and can be extended to experimentally determine losses by metallic layers from electrical contacts or other dissipation mechanisms, which are parameters of interest to a broader class of optoelectronic devices, not only PhC LEDs.

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Section: Discussionmentioning

confidence: 99%

Measurement of extraction and absorption parameters in GaN-based photonic-crystal light-emitting diodes

Matioli

Fleury

Rangel

et al. 2010

Journal of Applied Physics

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“…The diffraction of light by optical gratings (or photonic crystals (PhCs)) offers one possible polarization-preserving light-extraction mechanism, in addition to the high light-extraction efficiency demonstrated in GaN LEDs. 16,17 In this work, we embed periodically distributed air rods (embedded PhCs) within the LED structure to form a highly diffractive optical medium that offers high light-extraction efficiency. The coherent nature of the diffraction by PhCs not only retains the original polarization of light but also offers directional light extraction, resulting in high-brightness polarized LEDs.…”

Section: Introductionmentioning

confidence: 99%

High-brightness polarized light-emitting diodes

et al. 2012

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Light-emitting diodes are becoming the alternative for future general lighting applications, with huge energy savings compared to conventional light sources owing to their high efficiency and reliability. Polarized light sources would largely enhance the efficiency in a number of applications, such as in liquid-crystal displays, and also greatly improve contrast in general illumination due to the reduction in indirect glare. Here, we demonstrate light-emitting diodes presenting high-brightness polarized light emission by combining the polarization-preserving and directional extraction properties of embedded photonic-crystals applied to non-polar gallium nitride. A directional enhancement of up to 1.8-fold was observed in the total polarized light emission together with a high polarization degree of 88.7% at 465 nm. We discuss the mechanisms of polarized light emission in non-polar gallium nitride and the photonic-crystal design rules to further increase the light-emitting diode brightness. This work could open the way to polarized white-light emitters through their association with polarization-preserving down-converting phosphors. INTRODUCTIONDue to a continuously improved performance, light-emitting diodes (LEDs) are not only the major contender for future general lighting sources, 1 but also play an important role in a growing number of other applications-from backlight for high-efficiency televisions and mobile phone displays, to car lights and headlights-replacing the classical white sources owing to their high efficiency, brightness, reliability and low operation cost. Polarized light sources would largely improve the efficiency of most of these applications: from general illumination, with an improved contrast due to reduced glare, 2 which also minimizes eye discomfort and ultimately eye strain, 3 to highefficiency displays which operate through the spatial modulation of polarized light 4 (for completeness, we also note that polarized light and other forms of artificial light could be harmful for the life of animals and other species relying on natural light cycles to live 5 ). However, common light sources are usually unpolarized, since the electric field of the light emitted has no preferred orientation. This is also the case for most of the nitride-based LEDs commercialized nowadays. A strongly linearly polarized source, however, is obtained in m-plane GaN LEDs where the asymmetric in-plane biaxial stress on the quantum wells (QWs) orients the light emitting dipoles preferentially along the in-plane a direction. Non-polar m-plane GaN LEDs were first developed and more intensively investigated due to the possible reduction of polarization-induced electric fields in the QWs, which for c-plane GaN LEDs degrade their radiative recombination rate as a result of quantum confined stark effects. 6,7 Today, the

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“…In our calculations, we used two different blue LEDs, an ideal one having a perfect PCE of unity and another one with a state-of-the-art performance reported with a PCE of 81.3% 10 . Considering the near unity extraction efficiencies obtained recently 11,12 , the model also assumes all the generated photons manage to be outcoupled from the device unless absorbed. Another assumption is that there is a mirror at the bottom of the device (e.g., a metal film) so that all the photons are reflected from the bottom part.…”

Section: Computational Methodologymentioning

confidence: 99%

Power conversion and luminous efficiency performance of nanophosphor quantum dots on color-conversion LEDs for high-quality general lighting

2012

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For high-quality general lighting, a white light source is required to exhibit good photometric and colorimetric performance along with a high level of electrical efficiency. For example, a warm white shade is desirable for indoors, corresponding to correlated color temperatures ≤4000 K, together with color rendering indices ≥90. Additionally, the luminous efficacy of optical radiation (LER) should be high, preferably ≥380 lm/W opt . Conventional white LEDs cannot currently satisfy these requirements simultaneously. On the other hand, color-conversion white LEDs (WLEDs) integrated with quantum dots (QDs) can simultaneously reach such high levels of photometric and colorimetric performance. However, their electrical efficiency performance and limits have been unknown. To understand their potential of luminous efficiency (lm/W elect ), we modeled and studied different QD-WLED architectures based on layered QD films and QD blends, all integrated on blue LED chips. The architecture of red, yellow and green emitting QD films (in this order from the chip outwards) is demonstrated to outperform the rest. In this case, for photometrically efficient spectra, the maximum achievable LE is predicted to be 327 lm/W elect . Using a state-of-the-art blue LED reported with a power conversion efficiency (PCE) of 81.3%, the overall WLED PCE is shown to be 69%. To achieve LEs of 100, 150 and 200 lm/W elect , the required minimum quantum efficiencies of the color-converting QDs are found to be 39, 58 and 79%, respectively.

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High extraction efficiency light-emitting diodes based on embedded air-gap photonic-crystals

Abstract: Published Version

Cited by 97 publications

References 14 publications

Measurement of extraction and absorption parameters in GaN-based photonic-crystal light-emitting diodes

Measurement of extraction and absorption parameters in GaN-based photonic-crystal light-emitting diodes

High-brightness polarized light-emitting diodes

Power conversion and luminous efficiency performance of nanophosphor quantum dots on color-conversion LEDs for high-quality general lighting

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