由於發光二極體 ( LEDs ) 極具潛力的優點，使得它在取代傳統照明的應用上逐漸受到重視成為明日之星。隨著在研究與發展上的快速進步，更多有效率的結構設計使得LED的發光效率越來越好。但在LED內部量子效率已高達90% 以上的今天，其整體外部量子效率仍然和內部量子效率有段很大落差，主要還是受限於光取出效率不彰的影響。在這裡，我們証實分別應用奈米網狀氧化鋅 ( Nanomesh ZnO layer ) 及光子晶體 ( Photonic crystals, PC ) 於紅光及藍光LED可以達到提升光取出的目的，並利用奈米球微影術來製作這些奈米結構。相較於傳統的電子束微影，奈米球微影術的優點則是以更低廉的成本及較高產能來製作奈米結構。在奈米網狀氧化鋅應用於紅光LED的部份，和傳統的紅光LED比較之下，在20 mA下的光輸出功率可以提升達14%。另一方面，藉由ZnO和SiO2折射率漸變的結構設計也可以使光輸出功率增加達24%。光取出效率的提升是因為奈米網狀氧化鋅結構成功使得更多的光自界面處散射出來，而折射率漸變的結構能有效地減少界面全反射而增加光取出。在光子晶體應用於藍光LED的部份，利用奈米球微影搭配ICP乾式蝕刻技術，在p-GaN上製作出二維六角晶格GaN圓柱陣列之光子晶體結構。藉由計算光子晶體能帶，在同晶格周期下模擬並製作出兩種光子晶體結構，並研究其光子晶體能隙 ( Photonic bandgap, PBG ) 對於光取出之影響。其中，PC 150 nm於藍光發光波長有對應到光能隙，而PC 180 nm結構的則沒有對應光能隙。結果顯示，有符合光能隙之PC 150 nm的光輸出功率比沒有光能隙之PC 180 nm結構明顯高出13%。這代表利用光能隙的效應能使光子晶體於藍光LED上達到更進一步的光取出效率改善。

Light-emitting diodes ( LEDs ) are becoming an increasingly attractive alternative to conventional light sources due to their promising potential. Rapid progress in research and development is dedicated to improving LEDs performance through the use of more efficient structures. However, the external quantum efficiency of LEDs has a significant gap due to low light extraction, although internal quantum efficiency has been reach 90% above. Here, we demonstrate an improving in the light extraction of AlGaInP and GaN LEDs using nanomesh ZnO layers and photonic crystals, respectively. Instead of using conventional electron-beam lithography, the nanosphere lithography was utilized to fabricate these nano-scale structures of LEDs due to its high throughput and effective-cost. In part of AlGaInP LEDs with nanomesh ZnO layer, the light output power revealed an increase by 14% at 20 mA injection current. In additional, the graded refractive index structure of ZnO/SiO2 layers also enhanced light output about 24% as compared to conventional AlGaInP LEDs. The improving light extraction were attributed to more light scattering by nanomesh ZnO layer and reduce the total internal reflection at semi-air interface by graded index structure effectively . In part of PC GaN LEDs, the PC patterns with two-dimensional hexagonal-lattice GaN-pillar array were integrated on the p-GaN layer by nanosphere lithography and ICP dry etching. Two types PC structures under the same lattice constant of 220 nm by simulation results of two-dimensional plane-wave expansion were fabricated to study the effect of photonic bandgap ( PBG ) to light extraction. One is PC 150 nm designed to posses a PBG within the blue emission light, the other is PC 180 nm without PBG. The light output power of the PC 150 nm with PBG was significantly enhanced by 13% in comparison to the PC 180 nm without PBG. It indicated that the PC structure with PBG can get further enhancement of light extraction in GaN LEDs due to the PBG effect.

[1] H. J. Round, “A note on carborundum,” Electrical world, vol.49, no.6, pp. 309, 1907.
[2] N. Holonyak Jr. and S. F. Bevaqua, “Coherent (visible) light emission from GaAs1-xPx junctions,” Appl. Phys. Lett., vol. 1, pp.82-83, 1962.
[3] H. Amano, N. Sawaki, I. Akasaki, and T. Toyoda, “Metalorganic vapor phase epitaxial growth of a high quality GaN film using an AlN buffer layer,” Appl. Phys. Lett., vol.48, pp.353-355, 1986.
[4] Y. Koide, N. Itoh, K. Itoh, N. Sawaki, and I. Akasaki, “Effect of AlN buffer layer on AlGaN/a-Al2O3 heterepitaxial growth by metalorganic vapor phase epitaxy,” Jpn. J. Appl. Phys., vol.27, pp.1156-1161, 1988.
[5] I. Akasaki, H. Amano, Y. Koide, K. Kiramatsu, and N. Sawaki, "Effects of an AlN buffer layer on crystallographic structure and on electrical and optical properites of GaN and Ga1-xAlxN (0<x0.4) films grown on sapphire substrates by MOVPE," J. Crystal Growth, vol.98, pp.209-219, 1989.
[6] I. Akasaki, H. Amano, K. Hiramatsu, and N. Sawaki, “High efficiency blue LED utilizing GaN film with AlN buffer layer grown by MOVPE,” Inst. Phys. Conf. Ser., no.91, pp.633-636, 1988.
[7] H. Amano, M. Kito, K. Hiramatsu, and I. Akasaki, “p-type conduction in Mg-doped GaN treated with low-energy electron beam irradiation,” Jpn. J. Appl. Phys., vol. 28. pp. L2112-L2114, 1989.
[8] S. Nakamura, T. Mukai, M. Senoh, and N. Iwasa, “Thermal annealing effects on p-type Mg-doped GaN films,” Jpn. J. Appl. Phys., vol. 31, pp. L139-L142, 1992.
[9] C. P. Kuo, R. M. Fletcher, T. D. Osentowski, M. C. Lardizabal, M. G., Craford, and V. M. Robbins, “High performance AlInGaP visible light emitting diodes,” Appl. Phys. Lett., vol. 57, pp 2937-2939, 1990.
[10] S. Nakamura, M. Senoh, N. Iwasa, S. Nagahama, T. Yamada, T. Mukai, “Superbright Green InGaN Single-Quantum-Well-Structure Light-Enmitting Diodes,” Jpn. J. Appl. Phys. vol.34, pp.L1332-L1335, 1995.
[11] D. A. Steigerwald, J. C. Bhat, Dave Collins, Robert M. Fletcher, M. O. Holcomb, M. J. Ludowise, P. S. Martin, and S. L. Rudaz, “Illumination with solid state lighting technology,” IEEE J. Quantum Electron., vol. 8, pp. 310-320, 2002.
[12] E. F. Schubert and J. K. Kim, “Solid-state light sources getting smart,” Science, vol. 308, pp. 1274-1278, 2005.
[13] T. A. Truong, L. M. Campos, E. Matioli, I. Meinel, C. J. Hawker, C. Weisbuch, and P. M. Petroff, “Light extraction from GaN-based light emitting diode structures with a noninvasive tow-dimensional photonic crystal,” Appl. Phys. Lett., 94, 023101, 2009.
[14] E. F. Schubert, Light-Emitting Diodes, Cambridge University Press, Cambridge, 2003.
[15] C. M. Tsai, J. K. Sheu, W. C. Lai, Y. P. Hsu, P. T. Wang, C. T. Kuo, C. K. Kuo, S. J. Chang, and Y. K. Su, “Enhanced output power in GN-based LEDs with naturally textured surface grown by MOCVD,” IEEE Electron Device Lett., vol. 26, pp. 464-466, 2005.
[16] 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., vol. 84, pp. 855-857, 2004.
[17] W. C. Peng and Y. S. Wu, ‘Enhanced Light Output in Double Roughened GaN Light-Emitting Diodes via Various Texturing Treatments of Undoped-GaN Layer,” Jpn. J. Appl. Phys., Part 1, vol. 45, pp. 7709-7712, 2006.
[18] J. J. Chen, Y. K. Su, C. L. Lin, S. M. Chen, W. L. Li, and C. C. Kao, “Enhanced output power of GaN-based LEDs with nano-patterned sapphire substrates,” IEEE Photon. Technol. Lett., vol. 20, pp. 1193-1195, 2008.
[19] S. J. Chang, Y. K. Su, Y. C. Lin, R. W. Chuang, C. S. Chang, J. K. Sheu, T. C. Wen, S. C. Shei, C. W. Kuo, and D. H. Fang, Phys. Stat. Sol. (c), no. 7, pp. 2253-2256, 2003.
[20] R. H. Horng, W. K. Wang, S. C. Huang, S. Y. Huang, S. H. Lin, C. F. Lin, and D. S. Wuu, “Growth and characterization of 380-nm InGaN/AlGaN LEDs grown on patterned sapphire substrates,” J. Cryst. Growth, vol. 298, pp. 219-222, 2007.
[21] C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, S. C. Wang, C. C. Yu, and C. F. Lin, “Light–output enhancement in a nitride-based light-emitting diode with 22° undercut sidewalls”, IEEE Photon. Technol. Lett., vol. 17, pp. 19-21, 2005.
[22] J. Shakya, K. H. Kim, J. Y. Lin, and H. X. Jiang, “Enhanced light extraction in III-nitride ultraviolet photonic crystal light-emitting diodes,” Appl. Phys. Lett., vol. 85, pp. 142-144, 2004.
[23] J. J. Wierer, M. R. Krames, J. E. Epler, N. F. Gardner, M. G. Craford, J. R. Wendt, J. A. Simmons, and M. M. Sigalas, “InGaN/GaN quantum-well heterostructure light-emitting diodes employing photonic crystal structures,” Appl. Phys. Lett., vol. 84, pp. 3885-3887, 2004.
[24] Z. S. Zhang, B. Zhang, J. Xu, K. Xu, Z. J. Yang, Z. X. Qin, T. J. Yu, and D. P. Yu, “Effects of symmetry of GaN-based two-dimensional photonic crystal with quasicrystal lattices on enhancement of surface light extraction,” Appl. Phys. Lett., vol. 88, 171103, 2006.
[25] J. Y. Kim, M. K. Kwon, K. S. Lee, S. J. Parka, S. H. Kim and K. D. Lee, “Enhanced light extraction from GaN-based green light-emitting diode with photonic crystal”, Appl. Phys. Lett., vol. 91, 181109, 2007.
[26] S. J. Chang, C. S. Chang, Y. K. Su, R. W. Chuang, W. C. Lai, C. H. Kuo, Y. P. Hsu, Y. C. Lin, S. C. Shei, H. M. Lo, J. C. Ke, and J. K. Sheu, “Nitride-Based LEDs With an SPS Tunneling Contact Layer and an ITO Transparent Contact,” IEEE Photon. Technol. Lett., vol. 16, pp. 1002-1004, 2004.
[27] J. K. Sheu, Y. S. Lu, M. L. Lee, W. C. Lai, C. H. Kuo and C. J. Tun, “Enhanced efficiency of`GaN-based light-emitting diodes with periodic textured Ga-doped ZnO transparent contact layer,” Appl. Phys. Lett., vol. 90, 263511, 2007.
[28] J. Zhong, H. Chen, G. Saraf, Y. Lu, C. K. Choi, J. J. Song, D. M. Mackie and H. Shen, “Integrated ZnO nanotips on GaN light emitting diodes for enhanced emission efficiency,” Appl. Phys. Lett., vol. 90, 263515, 2007.
[29] E. Yablonovitch, “Inhibited Spontaneous Emission in Solid-State Physics and Electronics,” Phys. Rev. Lett., vol. 58, pp. 2059-2062, 1987.
[30] S. John, “Strong localization of photons in certain disordered dielectric superlattices,” Phys. Rev. Lett., vol. 58, pp. 2486-2489, 1987.
[31] L. P. Biro, Zs. Balint, K. Kertesz, Z. Vertesy, G. I. Mark, Z. E. Horvath, J. Balazs, D. Mehn, I. Kiricsi, V. Lousse, and J.-P. Vigneron, “Role of photonic-crystal-type structures in the thermal regulation of a Lycaenid butterfly sister species pair,” Phys. Rev., E 67, 021907, 2003.
[32] Thomas F. Krauss, Richard M. De La Rue and Stuart Brand, “Two-dimensional photonic bandgap structures operating at near-infrared wavelengths,” Nature, vol. 383, pp. 699-702, 1996.
[33] 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. vol. 78, pp. 3294-3297, 1997.
[34] M. Fujta, S. Takahashi, Y. Tanaka, T. Asano, and S. Noda, “Simultaneous inhibition and redistribution of spontaneous light emission in photonic crystals,” Science, vol. 308, pp. 1296-1298, 2005.
[35] M. Boroditsky, R. Vrijen, T. F. Krauss, R. Coccioli, R. Bhat, and E. Yablonovitch, “Spontaneous Emission Extraction and Purcell Enhancement from Thin-film 2-D Photonic Crystal,” IEEE Lightwave Technol., vol. 17, pp. 2096-2112, 1999.
[36] Oder, T. N., Kim, K. H., Lin, J. Y. and Jiang, H. X., “III-nitride photonic crystals,” Appl. Phys. Lett., vol. 83, pp. 1231-1233, 2003.
[37] J. J. Wierer, M. R. Krames, J. E. Epler, N. F. Gardner, and M. G. Craford, “InGaN/GaN quantum-well heterostructure light-emitting diodes employing photonic crystal structures,” Appl. Phys. Lett., vol. 84, pp. 3885-3887, 2004.
[38] K. Orita, S. Tamura, T. Takizawa, T. Ueda, M. Yuri, S. Takigawa and D. Ueda, “High-extraction-efficiency blue light-emitting diode using extended-pitch photonic crystal,” Jpn J. Appl. Phys., vol. 43, pp. 5809-5813, 2004.
[39] A. David, T. Fujii, B. Moran, S. Nakamura, S. P. DenBaars, and C. Weisbuch, “Photonic crystal laser lift-off GaN light-emitting diodes,” Appl. Phys. Lett., vol. 88, 133514, 2006.
[40] T. N. Oder, H. S. Kim, J. Y. Lin, and H. X. Jiang, “III-nitride blue and ultraviolet photonic crystal light emitting diodes,” Appl. Phys. Lett., vol. 84, pp. 466-468, 2004.
[41] D. H. Kim, C. O. Cho, Y. G. Roh, H. Jeon, and Y. S. Park, “Enhanced light extraction from GaN-based light-emitting diodes with holographically generated two-dimensional photonic crystal patterns,” Appl. Phys. Lett., vol. 87, 203508, 2005.
[42] Ja-Yeon Kim, Min-Ki Kwon, Ki-Sung Lee, and Seong-Ju Park, “Enhanced light extraction from GaN-based green light-emitting diode with photonic crystal,” Appl. Phys. Lett., vol. 91, 181109, 2007.
[43] Kyeong-Jae Byeon, Seon-Yong Hwang, and Heon Lee, “Fabrication of two-dimensional photonic crystal patterns on GaN-based light-emitting diodes using thermally curable monomer-based nanoimprint lithography,” Appl. Phys. Lett., vol. 91, 091106, 2007.
[44] Schaak, R. E.; Cable, R. E.; Leonard, B. M.; Norris, B. C. “Colloidal Crystal Microarrays and Two-Dimensional Superstructures: A Versatile Approach for Patterned Surface Assembly,” Langmuir, vol. 20, pp. 7293-7297, 2004.
[45] Velev, O. D.; Jede, T. A.; Lobo, R. F.; Lenhoff, A. M. “Porous silica via colloidal crystallization,” Nature, vol. 389, pp. 447-448, 1997.
[46] McLellan, J. M.; Geissler, M.; Xia, Y. N. “Edge Spreading Lithography and Its Application to the Fabrication of Mesoscopic Gold and Silver Rings,” J. Am. Chem. Soc., vol. 126, pp. 10830-10831, 2004.
[47] Falkner, J. C.; Turner, M. E.; Bosworth, J. K.; Trentler, T. J.; Johnson,J. E.; Lin, T. W.; Colvin, V. L., “Virus Crystals as Nanocomposite Scaffolds,” J. Am. Chem. Soc., vol. 127, pp. 5274-5275, 2005.
[48] H. W. Deckman and J. H. Dunsmuir, “Applications of surface textures produced with natural lithography,” J. Vac. Sci. Technol. B, Microelectron.Process. Phenom., vol. 1, no. 4, pp. 1109–1112, 1983.
[49] M. Winzer, M. Kleiber, N. Dix, and R. Wiesendanger, “Fabrication of nano-dot- and nano-ring-arrays by nanosphere lithography,” Appl. Phys. A, vol. 63, no. 6, pp. 617–619, 1996.
[50] Tae Sun Kim, Sang-Mook Kim, Yun Hee Jang, and Gun Young Jung, “Increase of light extraction from GaN based light emitting diodes incorporating patterned structure by colloidal lithography,” Appl. Phys. Lett. vol. 91, 171114, 2007.
[51] N. D. Denkov, O. D. Velev, P. A. Kralchevsky, I. B. Ivanov, H. Yoshimura, and K. Nagayama, “Two-dimensional crystallization,” Nature, vol. 361, 26, 1993.
[52] Ferenc Ja’rai-Szabo’, Simion As_tilean, Zolta’n Ne’da, “Understanding self-assembled nanosphere patterns”, Chemical Physics Letters, vol. 408, pp. 241–246, 2005.
[53] David J. Norris, Erin G, Arling, Linli Meng, Ruth Heiny and L. E. Scriven “Opaline Photonic Crystal: How does self-assembly work”, Adv. Mater., No.16, page 16, 2004.
[54] Seung-Man Yang, Se Gyu Jang, Dae-Geun Choi, Sarah Kim, and HyungKyun Yu “Nanomachining by colloidal lithography”, Adv. Mater., No.16, page 16, 2004.
[55] Ormonde A D, Hicks E C, Castillo J and Van Duyne, “Nanosphere lithography: fabrication of large area Ag nanoparticle arrays by convective self-assembly and their characterization by scanning UV–vis extinction spectroscopy”, Langmuir, vol. 20, pp. 6927–6931, 2004.
[56] Yan Xu, Garrett J. Schneider, Eric D. Wetzel, and Dennis W. Prather, “Fabrication of self-assembled photonic-crystal structures by centrifugation and spin-coating”, proceedings of SPIE - The International Society for Optical Engineering, vol. 5183, 2003.
[57] J. Rybczynski , U. Ebels , M. Giersig, “Large-scale, 2D arrays of magnetic nanoparticles”, Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 219, pp. 1-6, 2003.
[58] B. S. Flavel, J. G. Shapter, and J. S. Quinton, “Nanosphere Lithography Using Thermal Evaporation of Gold,” IEEE, pp. 578-581, 2006.
[59] Nancy H. Finkel, Brian G. Prevo, Orlin D. Velev, and Lin He, “Ordered Silicon Nanocavity Arrays in Surface-Assisted Desorption/Ionization Mass Spectrometry”, Analytical Chemistry, vol. 77, pp. 1088-1095, 2005.
[60] Y. Xia, B.Gates, Y. Yin, Y. Lu, "Monodispersed Colloidal Spheres: Old Materials with New Applications," Advanced Materials, 12(10), pp. 693-713, 2000.
[61] M. Geissler, Y. Xia, "Patterning: Principles and Some New evelopments,” Advanced Materials, 16(15), pp. 1249-1268, 2004.
[62] T. Jensen, M. Malinsky, C. Haynes, R. Van Duyne, "Nanosphere Lithography: Tunable Localized Surface Plasmon Resonance Spectra Of Silver Nanoparticles," Journal of Physical Chemistry B, vol. 104, pp. 10549-10556, 2000.
[63] M. D. B. Charlton, T. Lee, M. E. Zoorob, P. A. Shields, W. N. Wang, “Improving LED extraction efficiency through surface patterning,” Proc. of SPIE, vol. 6669, 666914, 2007.
[64] Choi H W, Chua S J, Raman A, Pan J S and Wee A T S, “Plasma-induced damage to n-type GaN,” Appl. Phys. Lett., vol. 77, pp.1795-1797, 2000.