Photonic crystal LEDs – designing light extraction

Wiesmann, Christopher; Bergenek, K.; Linder, N.; Schwarz, Uli

doi:10.1002/lpor.200810053

Cited by 250 publications

(200 citation statements)

References 90 publications

(122 reference statements)

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“…7b). 35 As can be seen in Fig. 7b, the simulated result clearly shows that both the addition of air voids and a thin (< 50 nm) AlN conformal layer do not have a substantial impact on the extraction efficiency.…”

Section: Resultsmentioning

confidence: 67%

Comparison of the Performance of Lateral and Vertical InGaN/GaN-Based Light-Emitting Diodes with GaN and AlN Nucleation Layers

Kang

Choi

Song

et al. 2015

ECS J. Solid State Sci. Technol.

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We investigated the effects of in situ GaN and sputtered AlN nucleation layers on the output power of GaN-based blue (445 nm) LEDs on patterned sapphire substrate (PSS) and planar sapphire substrates. Both the PSS LEDs and planar LEDs showed the same operation voltages, but the LEDs with the AlN layer had much lower reverse leakage current at −15 V. The LEDs with the AlN layer showed higher external quantum efficiency (EQE) at low current regions than those with the GaN nucleation layer. However, the AlN nucleation layer LEDs experienced a little more severe efficiency droop than did the GaN layer LEDs. It was shown that the AlN nucleation layer samples contained fewer defects than the GaN nucleation layer samples. The Raman spectral results showed that the AlN nucleation layer samples experienced higher compressive stress than the GaN nucleation layer samples. Simulation results also showed that both the AlN nucleation layer and air voids in the GaN nucleation layer samples hardly affected the light extraction efficiency. Based on the electrical, X-ray diffraction (XRD), cathodoluminescence (CL), and Raman results, the electrical behavior of the PSS and planar LEDs are described and discussed. InGaN/GaN-based light-emitting diodes (LEDs) are technologically important because of their use in a variety of emitting device applications, which cover wavelengths from green to ultraviolet (UV) spectra.1-4 Currently, high-brightness InGaN/GaN-based LEDs are commercially available. On the one hand, in order to realize general illumination application, the output performance of LEDs should be improved further. One of the major barriers to the enhancement of the light output efficiency of GaN-based LEDs is a high density of threading dislocations (TDs) (in the range of 10 8 -10 10 cm -2 ), 5 which are generated during GaN growth because of the large lattice mismatch and thermal expansion coefficient difference between GaN and sapphire substrate.6,7 Thus, it is crucial to develop ways of reducing TD density to enhance the light output performance. To minimize the generation of TDs, different methods have been proposed, including epitaxial lateral overgrowth (ELOG), [8][9][10][11] SiO 2 patterned mask, 12,13 and ELOG on patterned sapphire substrate (PSS). 14-19 Among them, ELOG on PSS are most commonly used to grow high-quality GaNbased epitaxial layers. For example, Kissinger et al., 15 investigating the output performance of blue LEDs fabricated on lens PSS (LPSS), reported that LPSS-LEDs exhibited 250% higher luminous intensity at an injection current of 20 mA than conventional LEDs and 117% higher emission angle than conventional LEDs. Wuu et al., 18 investigating the effect of hole-PSS on the output performance of near-UV GaN-based LEDs, reported that typical lamp-form PSS-LEDs had an external quantum efficiency of 14.1%, which is higher than that of conventional LEDs. The improvement was attributed to the decrease in TD density and the increase in light extraction efficiency. It is well known that the nucleation layer...

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Section: Resultsmentioning

confidence: 67%

Comparison of the Performance of Lateral and Vertical InGaN/GaN-Based Light-Emitting Diodes with GaN and AlN Nucleation Layers

Kang

Choi

Song

et al. 2015

ECS J. Solid State Sci. Technol.

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“…A power monitor was used to measure the power flux (P out ) passing through a plane placed above the top surface of LEDs, and a box monitor enclosing the dipole source was used to calculate the whole power emitted from the dipole source (P source ). Then the LEE of LEDs was defined as [28]:…”

Section: Model Of Simulation and Numerical Methodsmentioning

confidence: 99%

Using Three-Component Hierarchical Structures to Improve the Light Extraction From White Leds Based on Red-Green-Blue Color Mixing Method

Li¹,

Li²,

Kong³

et al. 2017

PIER C

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Abstract-In this work, we present a three-component hierarchical structure to simultaneously improve the red, green, and blue (RGB) light extraction efficiency (LEE) of white light-emitting diodes (LEDs) based on color mixing method. With the help of 3D finite-difference time-domain (FDTD) simulations, the effects of the embedded photonic crystals (PhCs) the normal surface PhCs and the nano-rods on the enhancement of RGB light extraction were investigated. The results were compared with those of the conventional planar LEDs and the normal surface PhCs LEDs over the whole visible spectrum. Results from the simulations demonstrated that the maximum LEE for the hierarchical structures LEDs gave 112%, 327%, and 284% RGB LEE enhancement, respectively, compared to that of the conventional planar LEDs, and achieved 104%, 191%, and 187% RGB LEE enhancement compared to that of LEDs with normal surface PhCs. The emission characteristics of the hierarchical structures LEDs were also revealed in detail by FDTD simulations. The results shown in this paper would do a favor for the design and fabrication of high efficiency LEDs.

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“…23,24 ( Fig. 3(b)) For a leaky harmonic, the in-plane wavevector is complex and thus the energy I(x) decays exponentially as the mode propagates in the x direction as…”

Section: Extraction Approachesmentioning

confidence: 99%

“…27 to model while the models for the distribution of photons in the surface roughened LEDs are still controversial. 23,24,28 Also, there are both theoretical and experimental work showing that PhC patterned unencapsulated LEDs have higher extraction coefficient than surface roughened LEDs. 24,27 Therefore, in this thesis, we will choose PhC patterned LED when it comes to unencapsulated devices.…”

Section: Extraction Approachesmentioning

confidence: 99%