High Extraction Efficiency GaN-Based Photonic-Crystal Light-Emitting Diodes: Comparison of Extraction Lengths between Surface and Embedded Photonic Crystals

Matioli, Elison; Fleury, Blaise; Rangel, Elizabeth; Melo, Thiago; Hu, Evelyn L.; Speck, James S.; Weisbuch, C.

doi:10.1143/apex.3.032103

Cited by 31 publications

(15 citation statements)

References 12 publications

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“…To effectively extract the guided light in the rather thick free-standing m-plane GaN substrates, the PhCs were placed within the LED structure, which increases their interaction with the guided modes (schematics in Figure 2a). 25 An improved diffraction efficiency is obtained by embedding air gaps within the GaN, which results in a large contrast in refractive index. The extraction of polarized light by embedded PhCs in m-plane GaN LEDs was further motivated by the high extraction efficiency previously observed in c-plane GaN LEDs.…”

Section: 24mentioning

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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Section: 24mentioning

confidence: 99%

High-brightness polarized light-emitting diodes

et al. 2012

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“…The measured extraction length for four diffraction vectors of fundamental guided modes is 109 lm (2G CX ), 93 lm (G X1M ), 123 lm (G CM ), and 122 lm (2G CM ), respectively, which matches the previous literature results. 15 These experimental determinations of the PhC extraction length indicated that the minimum device emission area of the GaN PhC l-uTFLED must be more than 1E4 square microns, which allows for extraction of all guided light. Through this analysis, the diffracted angle h out of the guided mode extraction characteristics from the GaN PhC l-uTFLEDs can be studied further when the PhC emission aperture sizes are less the 1E4 square microns.…”

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confidence: 94%

“…12,15 The linewidth of each diffracted guided mode is related to its extraction length, which serves as a probe of PhC modal extraction, as shown in Fig. 2.…”

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Emission aperture size limited the guided mode extraction characteristics of GaN-based ultrathin-film photonic crystal micro-light-emitting diodes

Lai

2012

Appl. Phys. Lett.

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“…An initial demonstration of bio-inspired compound eye structures (CESs) on GaP-based red LEDs showed excellent performance for light extraction efficiency [8]. Previously, the large indexcontrast embedded photonic crystals [9], [10], self-assembled colloidal MLAs [11], [12], [14], and concave microstructure arrays via imprinting methods [13] had been used for achieving improved light extraction over a large angular distribution, which in turn resulted in significant increase in light extraction efficiency in GaN-based LEDs (GaN LEDs). Similar concept by using colloidal MLAs had also been used for efficient extraction of both guided mode and substrate mode in organic LED [14].…”

Section: Introductionmentioning

confidence: 99%

Increased Light Extraction From GaN Light-Emitting Diodes by ${\rm SiN}_{{\rm x}}$ Compound Eyes

Kang

Song

Jang

et al. 2013

IEEE Photon. Technol. Lett.

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We demonstrate GaN-based blue light-emitting diodes (GaN LEDs) with artificial compound eye structures (CESs). The GaN LEDs consist of microlens arrays (MLAs) and antireflective subwavelength structures (SWSs). The CESs, formed on the LED surface by two-step pattern transfer of reflowed photoresist micro patterns and Ag nanoparticles, play an important role in enhancing the light extraction efficiency by reducing both the Fresnel and the total internal reflection. The CES integrated GaN LEDs show an output power enhancement of 93% compared to that of conventional GaN LEDs with flat surface, without any serious degradation of electrical characteristics. Optical simulations by ray-tracing and the rigorous coupled-wave analysis method provide design guidelines for MLAs and SWSs, respectively.Index Terms-GaN-based LEDs, light extraction efficiency, microlens, subwavelength structure, compound eye structures.

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High Extraction Efficiency GaN-Based Photonic-Crystal Light-Emitting Diodes: Comparison of Extraction Lengths between Surface and Embedded Photonic Crystals

Cited by 31 publications

References 12 publications

High-brightness polarized light-emitting diodes

High-brightness polarized light-emitting diodes

Emission aperture size limited the guided mode extraction characteristics of GaN-based ultrathin-film photonic crystal micro-light-emitting diodes

Increased Light Extraction From GaN Light-Emitting Diodes by ${\rm SiN}_{{\rm x}}$ Compound Eyes

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