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  • Editor: Bernard Kippelen
  • Vol. 19, Iss. S4 — Jul. 4, 2011
  • pp: A701–A709
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Design and fabrication of high-index-contrast self-assembled texture for light extraction enhancement in LEDs

Xing Sheng, Lirong Zeng Broderick, Juejun Hu, Li Yang, Anat Eshed, Eugene A. Fitzgerald, Jurgen Michel, and Lionel C. Kimerling  »View Author Affiliations


Optics Express, Vol. 19, Issue S4, pp. A701-A709 (2011)
http://dx.doi.org/10.1364/OE.19.00A701


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Abstract

We developed a high-index-contrast photonic structure for improving the light extraction efficiency of light-emitting diodes (LEDs) by a self-assembly approach. In this approach, a two-dimensional grating can be non-lithographically integrated on the top of virtually any types of LEDs with controlled structural parameters and material indices. As a proof of concept, our designed photonic structure was implemented on a GaAs double heterojunction LED. Using numerical electromagnetic simulations, we explored the effects of the structural parameters (the grating period, layer thickness and material indices) on the device performances, followed by fabrication through a self-assembled porous alumina as a template. Device simulation and experimental results indicate that an optimized high-index-contrast (a-Si / air) grating obtains a much larger efficiency increase than using a low-index SiO2 grating. In addition, the devices maintain a Lambertian radiation pattern with the self-assembled grating. This technique provides an effective and low-cost method for improving LED efficiency.

© 2011 OSA

1. Introduction

Light-emitting diodes (LEDs) have become an emerging and promising candidate for light sources. Unlike conventional incandescent or fluorescent light sources, LEDs directly transfer electricity into light. Therefore, it has many advantages such as high energy conversion efficiency, long lifetime and small footprint [1

1. M. R. Krames, O. B. Shchekin, R. Mueller-Mach, G. O. Mueller, L. Zhou, G. Harbers, and M. G. Craford, “Status and future of high-power light-emitting diodes for solid-state lighting,” J. Display Technol. 3(2), 160–175 (2007), http://www.opticsinfobase.org/jdt/abstract.cfm?URI=jdt-3-2-160. [CrossRef]

]. Typical LED devices are made of inorganic (III-V) or organic semiconductor junctions. The internal quantum efficiency η i of the light emission process, which is the portion of electron-hole pairs converted into photons, can be increased by improving material quality, and the state-of-the-art η i has reached 90%, already approaching the theoretical limit [2

2. I. Schnitzer, E. Yablonovitch, C. Caneau, and T. J. Gmitter, “Ultrahigh spontaneous emission quantum efficiency, 99.7% internally and 72% externally, from AlGaAs/GaAs/AlGaAs double heterostructures,” Appl. Phys. Lett. 62(2), 131–133 (1993), http://link.aip.org/link/doi/10.1063/1.109348. [CrossRef]

]. As a consequence, currently the major LED efficiency limiting factor becomes poor light extraction, i.e. photons trapped inside the device due to total internal reflection at semiconductor and air interface. For a planar LED, the light extraction efficiency η e can be estimated to be 1/4n 2 [3

3. E. Schubert, Light Emitting Diodes, (Cambridge University Press, 2006).

]. For most semiconductors, their refractive indices n are high (n > 2). Therefore, η e is a severe limitation for overall device performance.

To resolve the issue of limited extraction efficiency η e in semiconductor LEDs, many photonic designs have been proposed. For example, organic materials are used as encapsulants to cover the top surface and reduce the total internal reflection [4

4. C. J. Nuese, J. J. Tietjen, J. J. Gannon, and H. F. Gossenberger, “Optimization of electroluminescent efficiencies for vapor-grown GaAs1−xPx diodes,” J. Electrochem. Soc. 116(2), 248–253 (1969), http://dx.doi.org/10.1149/1.2411807. [CrossRef]

]. Another example is to roughen/texture the device surface and induce stronger scattering effect [5

5. O. B. Shchekin, J. E. Epler, T. A. Trottier, T. Margalith, D. A. Steigerwald, M. O. Holcomb, P. S. Martin, and M. R. Krames, “High performance thin-film flip-chip InGaN–GaN light-emitting diodes,” Appl. Phys. Lett. 89(7), 071109 (2006), http://link.aip.org/link/doi/10.1063/1.2337007. [CrossRef]

,6

6. T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855–857 (2004), http://link.aip.org/link/doi/10.1063/1.1645992. [CrossRef]

]. However, these methods have limitations. Organic encapsulants suffer from degradation under photon radiation (especially for blue and green light), which largely limits their use for long lifetime and high brightness LEDs. Texturing semiconductor surface (by plasma etching, for example) generates defects that work as recombination centers that exacerbate non-radiative recombination and decrease the internal quantum efficiency η i [7

7. H. S. Yang, S. Y. Han, K. H. Baik, S. J. Pearton, and F. Ren, “Effect of inductively coupled plasma damage on performance of GaN-InGaN multiquantum-well light-emitting diodes,” Appl. Phys. Lett. 86(10), 102104 (2005), http://link.aip.org/link/doi/10.1063/1.1882749. [CrossRef]

]. Furthermore, random scattering surfaces generated using a conventional texturing process lack the ability to purposively optimize and control the structural parameters of the textured surface.

Photonic crystal (PhC) has a structure with one, two, or three dimensional (1D, 2D and 3D) periodic patterns consisting of two materials with different refractive indices. In such periodic structures, light propagation can be controlled in various ways [8

8. S. Fan, P. R. Villeneuve, J. D. Joannopoulos, and E. F. Schubert, “High extraction efficiency of spontaneous emission from slabs of photonic crystals,” Phys. Rev. Lett. 78(17), 3294–3297 (1997), http://link.aps.org/doi/10.1103/PhysRevLett.78.3294. [CrossRef]

,9

9. A. A. Erchak, D. J. Ripin, S. Fan, P. Rakich, J. D. Joannopoulos, E. P. Ippen, G. S. Petrich, and L. A. Kolodziejski, “Enhanced coupling to vertical radiation using a two-dimensional photonic crystal in a semiconductor light-emitting diode,” Appl. Phys. Lett. 78(5), 563–565 (2001), http://link.aip.org/link/doi/10.1063/1.1342048. [CrossRef]

]. To increase LED extraction efficiency, a two-dimensional photonic crystal structure can be embedded in the device [10

10. E. Matioli, E. Rangel, M. Iza, B. Fleury, N. Pfaff, J. Speck, E. Hu, and C. Weisbuch, “High extraction efficiency light-emitting diodes based on embedded air-gap photonic-crystals,” Appl. Phys. Lett. 96(3), 031108 (2010), http://link.aip.org/link/doi/10.1063/1.3293442. [CrossRef]

] or integrated on top surface [11

11. J. J. Wierer, A. David, and M. M. Megens, “III-nitride photonic-crystal light-emitting diodes with high extraction efficiency,” Nat. Photonics 3(3), 163–169 (2009), http://www.nature.com/nphoton/journal/v3/n3/full/nphoton.2009.21.html. [CrossRef]

,12

12. M. Fujita, S. Takahashi, Y. Tanaka, T. Asano, and S. Noda, “Simultaneous inhibition and redistribution of spontaneous light emission in photonic crystals,” Science 308(5726), 1296–1298 (2005), http://www.sciencemag.org/content/308/5726/1296(abstract). [CrossRef] [PubMed]

]. Due to the periodicity, the guided waves can leak to free space as Bloch modes. Therefore, light can escape from the high index semiconductors even if the incident angle is larger than the critical angle. However, to fabricate these photonic crystals with submicron feature size, high-cost methods like interference lithography or electron beam lithography have to be employed, which prohibits LED cost reduction and high-volume production. Therefore, a low-cost and controllable method is highly desirable for fabrication of light extraction photonic crystal structures in LED devices.

Here, we proposed a self-assembled two-dimensional photonic structure to increase the light extraction efficiency in LEDs. The proposed structure has several advantages: (1) A potentially low-cost, self-assembled method is introduced for fabrication, and the structural parameters can be controlled by experimental conditions; (2) Unlike plasma or wet chemical etching, the method is non-specific and can be implemented on top of any semiconductors; (3) Instead of etching through the active device, the structure is directly deposited on the surface, so it is non-damaging and does not cause any degradation of internal quantum efficiency η i; (4) According to the targeted emission wavelength, various materials can be deposited to make the structure for achieving optimal light extraction; (5) As we will discuss below, a high-index-contrast texture is used, which provides much more efficient light extraction than low-index-contrast structures like SiO2 / air or Al2O3 / air gratings.

2. Device structure

The proposed photonic structure is integrated onto a conventional GaAs based LED, as shown in Fig. 1(a)
Fig. 1 (a) Schematic layout of a test LED device with photonic crystal structures integrated on top surface for light extraction. The active device is a double heterojunction based on a GaAs substrate. (b) Top view of the photonic crystal layer, which has a hexagonal lattice, with period Λ, thickness t and rod diameter D.
. A double heterojunction was grown on an n-type GaAs substrate by Metal-Organic Chemical Vapor Deposition (MOCVD). The detailed structure (from bottom to top) is 1 μm n-Al0.3Ga0.7As (Si doping, n = 4 × 1018 cm−3), 0.12 μm intrinsic GaAs and 1 μm p-Al0.3Ga0.7As (Zn doping, p = 4 × 1018 cm−3). Subsequently, a thin p-GaAs layer (200nm, Zn doping, p = 1 × 1019 cm−3) is grown on top of the p-i-n junction as a protecting layer to prevent the Al0.3Ga0.7As layer from oxidation and enable a better ohmic contact. Ideal ohmic contacts on the n-GaAs and p-GaAs are formed by 20 nm Ni / 30 nm Ge / 200 nm Au and 20 nm Ni / 30 nm Zn / 200 nm Au, followed by rapid thermal annealing (at 400 °C for 40 seconds). The above procedures create the reference LED device without light extraction structures.

The top view of designed light extraction configuration is plotted in Fig. 1(b), made by a hexagonal pattern as a grating layer. Due to the diffraction effect of the grating, light propagating at oblique angles (outside the emission cone) can be partly coupled out from the high index III-V semiconductor layer. Therefore, the light extraction efficiency will be significantly improved. Since the light out-coupling critically depends on the light extraction structure, the grating should be carefully designed to maximize the efficiency at the device emission wavelength.

3. Numerical simulation

3.1 Optimization of grating parameters

Here we show that the structure and optical parameters of the gratings (refractive index, grating period Λ, cylinder diameter D and thickness t in Fig. 1(b)) can significantly impact the light extraction efficiency. Here we assume the grating filling area ratio is 1:1, i.e., D = 0.74 Λ, and study the impact of varying Λ and t. To quantify the effect of grating index contrast, we simulated two types of gratings, amorphous silicon (a-Si) in air matrix and silicon dioxide (SiO2) in air matrix. Figure 2(a)
Fig. 2 Plot of the relative efficiency increase after introducing the grating layer for light extraction, as a function of grating period Λ and thickness t. The performance is compared with the planar device without the grating. Grating structure: (a) a-Si hexagonal pattern in air matrix; (b) SiO2 hexagonal pattern in air matrix.
and 2(b) plot the relative LED efficiency enhancement as functions of Λ and t for both types of gratings. Figure 2(a) reveals that when we choose appropriate values (Λ and t) for the a-Si / air grating, strong light extraction effect appears and the LED performance is enhanced. According to the simulation, the optimized design corresponds to Λ = 500 nm and t = 200 nm, where an enhancement factor of up to 70% can be achieved. Although the SiO2 / air grating has a similar optimized region (Λ = 600 nm and t = 250 nm), the optimal enhancement factor is much lower (about 18%). This suggests that the a-Si / air grating is very effective in enhancing light extraction, because of the high index contrast (4.0 versus 1.0) of this system as well as the transparency of a-Si in the near-infrared wavelength range. In comparison, the optimal enhancement is far less significant in the SiO2 / air grating design (Fig. 2(b)) due to the much lower index contrast (1.4 versus 1.0).

3.2 Calculation of far field emission profiles

To further understand the effects of high-index-contrast grating, we analyzed the far field emission pattern for the LED structure with the optimal grating parameters (a-Si / air grating with Λ = 500 nm and t = 200 nm). Figure 3
Fig. 3 Simulated far-field emission pattern at a wavelength of 870 nm. (a) Planar LED without grating on top, which shows a Lambertian pattern. (b) LED with a periodic a-Si / air grating of optimized parameters (Λ = 500 nm and t = 200 nm), which shows a non-Lambertian pattern. (c) Averaged angular dependence of light emission for devices without (green) and with (red) a-Si grating. The normalized intensity has an arbitrary unit.
compares the contour plots for the LEDs with and without grating in the reciprocal space. In Fig. 3(a) and 3(b), k x and k y are parallel to the device plane, and each point (k x, k y) corresponds to a specific emission angle θ in the far field,
sinθ=kx2+ky22π/λ0=kx2+ky2k0
(1)
The averaged angular dependences are plotted in Fig. 3(c). As expected, the planar device reveals a Lambertian emission pattern with a maximum in the normal direction, since GaAs has an isotropic spontaneous emission. For the LED with grating, the non-Lambertian behavior is caused by the outcoupling of the guided modes due to diffraction, which also explains the improvement of extraction efficiency. Because the results are averaged among dipoles emitting at different directions and combining both TE and TM modes, no significantly sharp peaks can be observed as mentioned in some references [11

11. J. J. Wierer, A. David, and M. M. Megens, “III-nitride photonic-crystal light-emitting diodes with high extraction efficiency,” Nat. Photonics 3(3), 163–169 (2009), http://www.nature.com/nphoton/journal/v3/n3/full/nphoton.2009.21.html. [CrossRef]

,15

15. C. F. Lai, J. Y. Chi, H. C. Kuo, H. H. Yen, C. E. Lee, C. H. Chao, W. Y. Yeh, and T. C. Lu, “far-field and near-field distribution of GaN-based photonic crystal LEDs with guided mode extraction,” IEEE J. Sel. Top. Quantum Electron. 15(4), 1234–1241 (2009), http://dx.doi.org/10.1109/JSTQE.2009.2015582. [CrossRef]

].

4. Fabrication and characterization of the self-assembled light extraction structures

The above simulation results predict and optimize the performance of devices with a perfectly periodic texture. To fabricate the optimized sub-micron light extraction structure on top of the LED devices, one needs to resort to lithographic techniques. If the light extraction structure only has short range order, the device performances will deviate from the simulations because of the average effect due to imperfection. However, the influences of different index contrast can still be observable in those short-range-order structures.

5. Experimental results and discussion

The electroluminescence (EL) performances of LEDs with different light extraction structures were measured using an optical multimeter (Ando AQ2140). A multimode fiber (100 μm diameter, NA = 0.28) was placed above the devices to collect the emitted photons from the surface. The light intensity-current (L-I) characteristics are shown in Fig. 5(a)
Fig. 5 Performances for LED devices with various top structures: the planar LED without grating (green), the LED with SiO2 grating (blue) and the LED with a-Si grating (red). (a) Light intensity-current (L-I) curves; (b) Emission spectra measured at current of 20 mA. It can be observed that the LED with a-Si grating shows the highest emission intensity, thus obtaining the highest efficiency. (c) Angular resolved measurement of light emission for the planar LED and the one with a-Si grating. The normalized intensity has an arbitrary unit.
. The slight non-linear behavior is due to some feedback mechanisms, causing a small portion of stimulated emission [19

19. T. Egawa, Y. Niwano, K. Fujita, K. Nitatori, T. Watanabe, T. Jimbo, and M. Umeno, “First fabrication of AlGaAs/GaAs double-heterostructure light-emitting diodes grown on GaAs(111)a substrates using only silicon dopant,” Jpn. J. Appl. Phys. 34(Part 1, No. 2B), 1270–1272 (1995), http://jjap.jsap.jp/link?JJAP/34/1270/. [CrossRef]

]. It can be clearly seen that the emission intensity is significantly higher if the designed grating is used as a light extraction structure. Compared to the planar device without any light extraction structure, the device with a-Si grating shows a relative efficiency improvement of 27%, while the SiO2 grating only achieves 7.3% relative increase. These results are further confirmed by the emission spectra measured under a current of 20 mA by an optical spectrum analyzer (Ando AQ6315A). As illustrated in Fig. 5(b), all the spectra peak at 870 nm, with a full width at half-maximum (FWHM) of 26 nm. The L-I curves and emission spectra clearly reveal that the grating with higher index contrast entails higher performance for light extraction, which agrees well with our numerical predictions. Other approaches show a 130% increase in GaN devices by surface roughening [6

6. T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855–857 (2004), http://link.aip.org/link/doi/10.1063/1.1645992. [CrossRef]

] and 39% increase in AlGaInP directly using the low-index AAO [17

17. C. C. Liu, S. X. Lin, C. C. Wang, K. K. Chong, C. I. Hung, and M. P. Houng, “Light output enhancement of AlGaInP light emitting diodes with nanopores of anodic alumina,” Jpn. J. Appl. Phys. 48(8), 082102–082104 (2009), http://jjap.jsap.jp/link?JJAP/48/082102/. [CrossRef]

]. The differences in materials systems (GaAs vs. GaN or AlGaInP) and device configurations (bulk vs. thin film) lead to lower efficiency improvements in our case. However, our approach can be implemented in those different systems and will yield better performances which scale with index-contrast and structural parameters according to our model.

Figure 5(c) shows the angular dependence of emission for the devices with and without a-Si grating. In the measurement, the devices are mounted on a goniometer which can rotate 90 degrees. Unexpectedly, both the devices show a Lambertian emission pattern, which does not fully agree with the simulation predictions shown in Fig. 3(c). This is mainly due to the imperfection of the fabricated grating. As seen in the SEM image of AAO membrane (Fig. 4(a)), the pore distribution only exhibits short-range order. In addition, the AFM images of the deposited a-Si and SiO2 indicate we obtained a cone-shaped array. Therefore, the self-assembled approach causes a deviation from the ideal hexagonal array of cylinders, thus inducing random scattering and forming the near-Lambertian emission pattern [20

20. W. H. Koo, S. M. Jeong, F. Araoka, K. Ishikawa, S. Nishimura, T. Toyooka, and H. Takezoe, “Light extraction from organic light-emitting diodes enhanced by spontaneously formed buckles,” Nat. Photonics 4(4), 222–226 (2010), http://www.nature.com/nphoton/journal/v4/n4/abs/nphoton.2010.7.html. [CrossRef]

].

Although the above results are obtained from GaAs based near-IR LEDs, the proposed design can also be applied for light extraction in LEDs emitting at other spectral ranges. For visible LEDs based on nitride or organic semiconductors, the simulation and fabrication methods we utilized here are still applicable, while the structural parameters should be altered to accommodate the target wavelength. The AAO template has controllable feature sizes, which can be manipulated by varying experimental conditions like applied voltage and anodization time [21

21. H. Masuda and K. Fukuda, “Ordered metal nanohole arrays made by a two-step replication of honeycomb structures of anodic alumina,” Science 268(5216), 1466–1468 (1995), http://www.sciencemag.org/content/268/5216/1466.short. [CrossRef] [PubMed]

]. It should be noted that a-Si becomes strongly absorptive at visible wavelengths (< 700 nm). Therefore, other materials should be exploited to make the self-assembled pattern. Possible candidates can be SiC and ZnS, both of which have high refractive indices as well as low absorption coefficients in the visible range [14

14. E. Palik, Handbook of Optical Constants of Solids (Academic Press, 1998).

].

6. Conclusion

In this paper, a self-assembled light extraction structure was integrated for LED efficiency enhancement. Based on numerical simulations, we systematically investigated the impact of grating parameters and materials selection on the light extraction. We showed that high-index gratings are far more effective in light extraction improvement compared to their low-index counterpart. The optimized structures were integrated on GaAs based LEDs by using self-assembled AAO membranes as a template, which acts as an effective and low-cost alternative to lithographic fabrications. The LED device with the optimized high-index-contrast a-Si grating yielded a 27% improvement in emission intensity. The effects of different index contrasts were verified by comparing the performances of gratings made from a-Si and SiO2. Unlike the simulation results, the device with fabricated a-Si grating showed a Lambertian emission pattern, which is due to the non-ideality of the periodicity. By proper structure design and materials selection, these approaches could also provide a guideline for efficiency enhancement in nitride and organic based LEDs.

Acknowledgments

The authors would like to thank Massachusetts Institute of Technology Energy Initiative (MITEI) Seed Fund Program for financial support.

References and links

1.

M. R. Krames, O. B. Shchekin, R. Mueller-Mach, G. O. Mueller, L. Zhou, G. Harbers, and M. G. Craford, “Status and future of high-power light-emitting diodes for solid-state lighting,” J. Display Technol. 3(2), 160–175 (2007), http://www.opticsinfobase.org/jdt/abstract.cfm?URI=jdt-3-2-160. [CrossRef]

2.

I. Schnitzer, E. Yablonovitch, C. Caneau, and T. J. Gmitter, “Ultrahigh spontaneous emission quantum efficiency, 99.7% internally and 72% externally, from AlGaAs/GaAs/AlGaAs double heterostructures,” Appl. Phys. Lett. 62(2), 131–133 (1993), http://link.aip.org/link/doi/10.1063/1.109348. [CrossRef]

3.

E. Schubert, Light Emitting Diodes, (Cambridge University Press, 2006).

4.

C. J. Nuese, J. J. Tietjen, J. J. Gannon, and H. F. Gossenberger, “Optimization of electroluminescent efficiencies for vapor-grown GaAs1−xPx diodes,” J. Electrochem. Soc. 116(2), 248–253 (1969), http://dx.doi.org/10.1149/1.2411807. [CrossRef]

5.

O. B. Shchekin, J. E. Epler, T. A. Trottier, T. Margalith, D. A. Steigerwald, M. O. Holcomb, P. S. Martin, and M. R. Krames, “High performance thin-film flip-chip InGaN–GaN light-emitting diodes,” Appl. Phys. Lett. 89(7), 071109 (2006), http://link.aip.org/link/doi/10.1063/1.2337007. [CrossRef]

6.

T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855–857 (2004), http://link.aip.org/link/doi/10.1063/1.1645992. [CrossRef]

7.

H. S. Yang, S. Y. Han, K. H. Baik, S. J. Pearton, and F. Ren, “Effect of inductively coupled plasma damage on performance of GaN-InGaN multiquantum-well light-emitting diodes,” Appl. Phys. Lett. 86(10), 102104 (2005), http://link.aip.org/link/doi/10.1063/1.1882749. [CrossRef]

8.

S. Fan, P. R. Villeneuve, J. D. Joannopoulos, and E. F. Schubert, “High extraction efficiency of spontaneous emission from slabs of photonic crystals,” Phys. Rev. Lett. 78(17), 3294–3297 (1997), http://link.aps.org/doi/10.1103/PhysRevLett.78.3294. [CrossRef]

9.

A. A. Erchak, D. J. Ripin, S. Fan, P. Rakich, J. D. Joannopoulos, E. P. Ippen, G. S. Petrich, and L. A. Kolodziejski, “Enhanced coupling to vertical radiation using a two-dimensional photonic crystal in a semiconductor light-emitting diode,” Appl. Phys. Lett. 78(5), 563–565 (2001), http://link.aip.org/link/doi/10.1063/1.1342048. [CrossRef]

10.

E. Matioli, E. Rangel, M. Iza, B. Fleury, N. Pfaff, J. Speck, E. Hu, and C. Weisbuch, “High extraction efficiency light-emitting diodes based on embedded air-gap photonic-crystals,” Appl. Phys. Lett. 96(3), 031108 (2010), http://link.aip.org/link/doi/10.1063/1.3293442. [CrossRef]

11.

J. J. Wierer, A. David, and M. M. Megens, “III-nitride photonic-crystal light-emitting diodes with high extraction efficiency,” Nat. Photonics 3(3), 163–169 (2009), http://www.nature.com/nphoton/journal/v3/n3/full/nphoton.2009.21.html. [CrossRef]

12.

M. Fujita, S. Takahashi, Y. Tanaka, T. Asano, and S. Noda, “Simultaneous inhibition and redistribution of spontaneous light emission in photonic crystals,” Science 308(5726), 1296–1298 (2005), http://www.sciencemag.org/content/308/5726/1296(abstract). [CrossRef] [PubMed]

13.

D. Delbeke, P. Bienstman, R. Bockstaele, and R. Baets, “Rigorous electromagnetic analysis of dipole emission in periodically corrugated layers: the grating-assisted resonant-cavity light-emitting diode,” J. Opt. Soc. Am. A 19(5), 871–880 (2002), http://www.opticsinfobase.org/abstract.cfm?URI=josaa-19-5-871. [CrossRef]

14.

E. Palik, Handbook of Optical Constants of Solids (Academic Press, 1998).

15.

C. F. Lai, J. Y. Chi, H. C. Kuo, H. H. Yen, C. E. Lee, C. H. Chao, W. Y. Yeh, and T. C. Lu, “far-field and near-field distribution of GaN-based photonic crystal LEDs with guided mode extraction,” IEEE J. Sel. Top. Quantum Electron. 15(4), 1234–1241 (2009), http://dx.doi.org/10.1109/JSTQE.2009.2015582. [CrossRef]

16.

K. Kim, J. Choi, T. S. Bae, M. Jung, and D. H. Woo, “Enhanced light extraction from nanoporous surfaces of InGaN/GaN-based light emitting diodes,” Jpn. J. Appl. Phys. 46(No. 10A), 6682–6684 (2007), http://jjap.jsap.jp/link?JJAP/46/6682/. [CrossRef]

17.

C. C. Liu, S. X. Lin, C. C. Wang, K. K. Chong, C. I. Hung, and M. P. Houng, “Light output enhancement of AlGaInP light emitting diodes with nanopores of anodic alumina,” Jpn. J. Appl. Phys. 48(8), 082102–082104 (2009), http://jjap.jsap.jp/link?JJAP/48/082102/. [CrossRef]

18.

X. Sheng, J. Liu, I. Kozinsky, A. M. Agarwal, J. Michel, and L. C. Kimerling, “Design and non-lithographic fabrication of light trapping structures for thin film silicon solar cells,” Adv. Mater. (Deerfield Beach Fla.) 23(7), 843–847 (2011), http://onlinelibrary.wiley.com/doi/10.1002/adma.201003217/abstract. [CrossRef]

19.

T. Egawa, Y. Niwano, K. Fujita, K. Nitatori, T. Watanabe, T. Jimbo, and M. Umeno, “First fabrication of AlGaAs/GaAs double-heterostructure light-emitting diodes grown on GaAs(111)a substrates using only silicon dopant,” Jpn. J. Appl. Phys. 34(Part 1, No. 2B), 1270–1272 (1995), http://jjap.jsap.jp/link?JJAP/34/1270/. [CrossRef]

20.

W. H. Koo, S. M. Jeong, F. Araoka, K. Ishikawa, S. Nishimura, T. Toyooka, and H. Takezoe, “Light extraction from organic light-emitting diodes enhanced by spontaneously formed buckles,” Nat. Photonics 4(4), 222–226 (2010), http://www.nature.com/nphoton/journal/v4/n4/abs/nphoton.2010.7.html. [CrossRef]

21.

H. Masuda and K. Fukuda, “Ordered metal nanohole arrays made by a two-step replication of honeycomb structures of anodic alumina,” Science 268(5216), 1466–1468 (1995), http://www.sciencemag.org/content/268/5216/1466.short. [CrossRef] [PubMed]

OCIS Codes
(230.3670) Optical devices : Light-emitting diodes
(250.0250) Optoelectronics : Optoelectronics

ToC Category:
Light-Emitting Diodes

History
Original Manuscript: March 28, 2011
Revised Manuscript: May 13, 2011
Manuscript Accepted: May 16, 2011
Published: May 19, 2011

Citation
Xing Sheng, Lirong Zeng Broderick, Juejun Hu, Li Yang, Anat Eshed, Eugene A. Fitzgerald, Jurgen Michel, and Lionel C. Kimerling, "Design and fabrication of high-index-contrast self-assembled texture for light extraction enhancement in LEDs," Opt. Express 19, A701-A709 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-S4-A701


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