我們成功地藉由奈米金粒子(Au nanoparticles)的局部化表面電漿效應(localized surface-plasmon resonance)，增強不管是光致放光(photoluminescence, PL)量測還是電致放光(electroluminescence, EL)量測上氧化鋅微米球之近能帶(Near band edge)放光。相反地，氧化鋅的缺陷放光則有明顯的被降低，這種螢光增強效果是來自於局部化表面電漿子共振效應的影響，使得氧化鋅內電子能於導電帶(Conduction band)與缺陷能階(Defect level)之間轉換。由時間解析的光致放光(Time-resolved PL)光譜量測結果顯示氧化鋅的自發放射速率(spontaneous rate)確實和氧化鋅的激子(excitons)與奈米金粒子的表面電漿耦合有關係，而這也是另一個氧化鋅微米球之近能帶放光被增強的原因。在利用n型氧化鋅微米球與p型氮化鎵(P-GaN)所製成之電致放光元件中，奈米金粒子表面電漿子共振效應亦增強氧化鋅之近能帶放光強度約增強6倍左右。為了更進一步了解奈米金粒子在電致放光元件中所扮演角色，我們也分別將奈米金粒子鍍在元件中不同位置來觀察其電致放光增強效果。上述表面電漿子共振增強效應機制可於未來應用於固態發射元件上，改善元件之放光特性並且增加其放光效率。

This paper demonstrates that both intensities of photoluminescence (PL) and electroluminescence (EL) from the band edge emission of ZnO submicron spheres can be improved by the use of localized surface-plasmon resonance (LSPR) Au nanoparticles (NPs). Conversely, the use of LSPR reduces the green emission from the surface defect of ZnO. The origin of such luminescence enhancement is attributed to the LSPR, where electrons transfer between a conduction band and defect level through the LSPR. Time-resolved PL measurement results reveal that the spontaneous rate is increased as a result of the coupling between ZnO excitons and Au NPs LSPR. The other reason for the enhancement of PL from the near-band-edge emission of ZnO is the exciton-LSP coupling between Au NPs and ZnO. A six-fold ultraviolet EL enhancement was achieved from the Au NPs decorated device. Different deposited sequences of Au NPs in an n-ZnO/p-GaN layer were made to understand the selective enhancement of EL. Enhancement such as the ones demonstrated in this paper should be considered in the future when designing the highly efficient solid state emitters.

Reference
[1] M. A. Abbasi, Z. H. Ibupoto, M. Hussain, O. Nur, and M. Willander, "The fabrication of white light-emitting diodes using the n-ZnO/NiO/p-GaN heterojunction with enhanced luminescence," Nanoscale Res. Lett. 8, 320 (2013).
[2] O. Lupan, T. Pauporte, and B. Viana, "Low-voltage UV-electroluminescence from ZnO-nanowire array/p-GaN light-emitting diodes," Adv. Mater. 22, 3298 (2010).
[3] Y. P. Hsieh, H. Y. Chen, M. Z. Lin, S. C. Shiu, M. Hofmann, M. Y. Chern, et al., "Electroluminescence from ZnO/Si-Nanotips Light-Emitting Diodes," Nano Lett. 9, 1839 (2009).
[4] J. Y. Wang, C. Y. Lee, Y. T. Chen, C. T. Chen, Y. L. Chen, C. F. Lin, et al., "Double side electroluminescence from p-NiO/n-ZnO nanowire heterojunctions," Appl. Phys. Lett. 95, 131117 (2009).
[5] A. Tsukazaki, A. Ohtomo, T. Onuma, M. Ohtani, T. Makino, M. Sumiya, et al., "Repeated temperature modulation epitaxy for p-type doping and light-emitting diode based on ZnO," Nat. Mater. 4, 42 (2005).
[6] J. H. Lim, C. K. Kang, K. K. Kim, I. K. Park, D. K. Hwang, and S. J. Park, "UV electroluminescence emission from ZnO light‐emitting diodes grown by high‐temperature radiofrequency sputtering," Adv. Mater. 18, 2720 (2006).
[7] H. Zeng, G. Duan, Y. Li, S. Yang, X. Xu, and W. Cai, "Blue luminescence of ZnO nanoparticles based on non-equilibrium processes: defect origins and emission controls," Adv. Funct. Mater. 20, 561 (2010).
[8] M. D. McCluskey and S. J. Jokela, "Defects in ZnO," J. Appl. Phys. 106, 071101, (2009).
[9] A. Janotti and C. G. Van de Walle, "Native point defects in ZnO," Phys. Rev. B 76, 165202 (2007).
[10] H. Zhu, C. X. Shan, B. Yao, B. H. Li, J. Y. Zhang, Z. Z. Zhang, et al., "Ultralow-Threshold Laser Realized in Zinc Oxide," Adv. Mater. 21, 1613 (2009).
[11] C. Cheng, E. Sie, B. Liu, C. Huan, T. Sum, H. Sun, et al., "Surface plasmon enhanced band edge luminescence of ZnO nanorods by capping Au nanoparticles," Appl. Phys. Lett. 96, 071107 (2010).
[12] J. F. Lu, C. X. Xu, J. Dai, J. T. Li, Y. Y. Wang, Y. Lin, et al., "Plasmon-enhanced whispering gallery mode lasing from hexagonal Al/ZnO microcavity," ACS Photonics 2, 73 (2015).
[13] S. G. Zhang, X. W. Zhang, Z. G. Yin, J. X. Wang, F. T. Si, H. L. Gao, et al., "Optimization of electroluminescence from n-ZnO/AlN/p-GaN light-emitting diodes by tailoring Ag localized surface plasmon," J. Appl. Phys. 112, 013112 (2012).
[14] Y. J. Lu, J. Kim, H. Y. Chen, C. H. Wu, N. Dabidian, C. E. Sanders, et al., "Plasmonic nanolaser using epitaxially grown silver film," Science 337, 450 (2012).
[15] A. Campion and P. Kambhampati, "Surface-enhanced Raman scattering," Chem. Soc. Rev. 27, 241 (1998).
[16] D. Schaadt, B. Feng, and E. Yu, "Enhanced semiconductor optical absorption via surface plasmon excitation in metal nanoparticles," Appl. Phys. Lett. 86, 063106 (2005).
[17] C. W. Lai, J. An, and H. C. Ong, "Surface-plasmon-mediated emission from metal-capped ZnO thin films," Appl. Phys. Lett. 86, 251105 (2005).
[18] S. G. Zhang, X. W. Zhang, Z. G. Yin, J. X. Wang, J. J. Dong, H. L. Gao, et al., "Localized surface plasmon-enhanced electroluminescence from ZnO-based heterojunction light-emitting diodes," Appl. Phys. Lett. 99, 181116 (2011).
[19] W. Z. Liu, H. Y. Xu, C. L. Wang, L. X. Zhang, C. Zhang, S. Y. Sun, et al., "Enhanced ultraviolet emission and improved spatial distribution uniformity of ZnO nanorod array light-emitting diodes via Ag nanoparticles decoration," Nanoscale 5, 8634 (2013).
[20] X. H. Li, Y. Zhang, and X. J. Ren, "Effects of localized surface plasmons on the photoluminescence properties of Au-coated ZnO films," Opt. Express 17, 8735 (2009).
[21] T. Singh, D. Pandya, and R. Singh, "Surface plasmon enhanced bandgap emission of electrochemically grown ZnO nanorods using Au nanoparticles," Thin Solid Films 520, 4646 (2012).
[22] Y. H. Lee, D. H. Kim, K. H. Yoo, and T. W. Kim, "Efficiency enhancement of organic light-emitting devices due to the localized surface plasmonic resonant effect of Au nanoparticles embedded in ZnO nanoparticles," Appl. Phys. Lett. 105, 183303 (2014).
[23] L. Jian Ming, L. Hsia Yu, C. Chung Liang, and C. Yang Fang, "Giant enhancement of bandgap emission of ZnO nanorods by platinum nanoparticles," Nanotechnology 17, 4391 (2006).
[24] S. S. Chen, X. H. Pan, H. P. He, W. Chen, W. Dai, C. Chen, et al., "60-fold photoluminescence enhancement in Pt nanoparticle-coated ZnO films: role of surface plasmon coupling and conversion of non-radiative recombination," Opt. Lett. 40, 2782 (2015).
[25] D. Y. Lei and H. C. Ong, "Enhanced forward emission from ZnO via surface plasmons," Appl. Phys. Lett. 91, 211107 (2007).
[26] J. F. Lu, Z. L. Shi, Y. Y. Wang, Y. Lin, Q. X. Zhu, Z. S. Tian, et al., "Plasmon-enhanced electrically light-emitting from ZnO Nanorod Arrays/p-GaN heterostructure devices," Sci Rep 6, 25645 (2016).
[27] C. W. Cheng, E. J. Sie, B. Liu, C. H. A. Huan, T. C. Sum, H. D. Sun, et al., "Surface plasmon enhanced band edge luminescence of ZnO nanorods by capping Au nanoparticles," Appl. Phys. Lett. 96, 071107 (2010).
[28] B. Niu, L. Wu, W. Tang, X. Zhang, and Q. Meng, "Enhancement of near-band edge emission of Au/ZnO composite nanobelts by surface plasmon resonance," CrystEngComm 13, 3678 (2011).
[29] Y. Lin, J. Li, C. Xu, X. Fan, and B. Wang, "Localized surface plasmon resonance enhanced ultraviolet emission and F-P lasing from single ZnO microflower," Appl. Phys. Lett. 105, 142107 (2014).
[30] Z. X. Chen, B. Y. Lai, J. M. Zhang, G. P. Wang, and S. Chu, "Hybrid material based on plasmonic nanodisks decorated ZnO and its application on nanoscale lasers," Nanotechnology 25, 295203 (2014).
[31] A. P. Abiyasa, S. F. Yu, S. P. Lau, E. S. P. Leong, and H. Y. Yang, "Enhancement of ultraviolet lasing from Ag-coated highly disordered ZnO films by surface-plasmon resonance," Appl. Phys. Lett. 90, 231106 (2007).
[32] W. Tang, D. Huang, L. Wu, C. Zhao, L. Xu, H. Gao, et al., "Surface plasmon enhanced ultraviolet emission and observation of random lasing from self-assembly Zn/ZnO composite nanowires," Crystengcomm 13, 2336 (2011).
[33] C. S. Wang, H. Y. Lin, J. M. Lin, and Y. F. Chen, "Surface-plasmon-enhanced ultraviolet random lasing from ZnO nanowires assisted by Pt nanoparticles," Appl. Phys. Express 5, 62003 (2012).
[34] T. Nakamura, S. Sonoda, and S. Adachi, "Plasmonic control of ZnO random lasing characteristics," Laser Phys. Lett. 11, 016004 (2014).
[35] S. G. Zhang, X. W. Zhang, Z. G. Yin, J. X. Wang, J. J. Dong, H. L. Gao, et al., "Localized surface plasmon-enhanced electroluminescence from ZnO-based heterojunction light-emitting diodes," Appl. Phys. Lett. 99, 181116 (2011).
[36] C. L. C. H. Y. Lin, Y. Y. Chou, L. L. Huang, Y. F. Chen, and K. T. Tsen "Enhancement of band gap emission stimulated by defect loss," Opt. Express 14, 2372 (2006).
[37] V. Subramanian, E. E. Wolf, and P. V. Kamat, "Green emission to probe photoinduced charging events in ZnO-Au nanoparticles. Charge distribution and fermi-level equilibration," J. Phys. Chem. B 107, 7479 (2003).
[38] Y. J. Fang, J. Sha, Z. L. Wang, Y. T. Wan, W. W. Xia, and Y. W. Wang, "Behind the change of the photoluminescence property of metal-coated ZnO nanowire arrays," Appl. Phys. Lett. 98, 033103 (2011).
[39] M. K. Lee, T. G. Kim, W. Kim, and Y. M. Sung, "Surface plasmon resonance (SPR) electron and energy transfer in noble metal−zinc oxide composite nanocrystals," J. Phys. Chem. C 112, 10079 (2008).
[40] H. M. Cheng, "Low-dimensional ZnO nanostructures: fabrication, optical properties and applications for dye-sensitied solar cells," dissertation, National Chiao Tung University, (2011).
[41] D. C. Reynolds, D. C. Look, and B. Jogai, "Optically pumped ultraviolet lasing from ZnO," Solid State Commun. 99, 873 (1996).
[42] R. M. Hewlett and M. A. McLachlan, "Surface structure modification of ZnO and the impact on electronic properties," Adv. Mater. 28, 3893 (2016).
[43] T. F. Dai, W. C. Hsu, and H. C. Hsu, "Improvement of photoluminescence and lasing properties in ZnO submicron spheres by elimination of surface-trapped state," Opt. Express 22, 27169 (2014).
[44] B. K. Meyer, H. Alves, D. M. Hofmann, W. Kriegseis, D. Forster, F. Bertram, et al., "Bound exciton and donor-acceptor pair recombinations in ZnO," Phys. Status Solidi B-Basic Solid State Phys. 241, 231 (2004).
[45] A. B. Djurišić and Y. H. Leung, "Optical properties of ZnO nanostructures," Small 2, 944 (2006).
[46] M. Liu, A. H. Kitai, and P. Mascher, "Point-defects and luminescence-centers in zinc-oxide and zinc-oxide doped with manganese," J. Lumines. 54, 35 (1992).
[47] L. Bixia, F. Zhuxi, and J. Yunbo, "Green luminescent center in undoped zinc oxide films deposited on silicon substrates," Appl. Phys. Lett. 79, 943 (2001).
[48] Mark Fox, "Optical properties of solids," 2nd, OXFORD,(2010).
[49] Y. Lin, X. Q. Liu, T. Wang, C. Chen, H. Wu, L. Liao, et al., "Shape-dependent localized surface plasmon enhanced UV-emission from ZnO grown by atomic layer deposition," Nanotechnology 24, 125705 (2013).
[50] K. A. Willets and R. P. Van Duyne, "Localized surface plasmon resonance spectroscopy and sensing," Annu. Rev. Phys. Chem. 58, 267 (2007).
[51] 吳民耀, 劉威志, "表面電漿子理論與模擬," 物理雙月刊:二十八卷二期, 486 (2006).
[52] E. Hutter and J. H. Fendler, "Exploitation of localized surface plasmon resonance," Adv. Mater. 16, 1685 (2004).
[53] D. A. Neamen, "Semiconductor physics and devices:basic principles," McGraw-Hill, (2011).
[54] S. O. Kasap, "Optoelectronics and photonics:principles and practices," 2nd, PEARSON, (2013).
[55] 郭浩中, 賴芳儀, 郭守義," LED原理與應用," 五南圖書出版公司, ( 2012).
[56] H. C. Hsu, H. Y. Huang, M. O. Eriksson, T. F. Dai, and P. O. Holtz, "Surface related and intrinsic exciton recombination dynamics in ZnO nanoparticles synthesized by a sol-gel method," Appl. Phys. Lett. 102, 013109 (2013).
[57] E. W. Seelig, B. Tang, A. Yamilov, H. Cao, and R. P. H. Chang, "Self-assembled 3D photonic crystals from ZnO colloidal spheres," Mater. Chem. Phys. 80, 257 (2003).
[58] H. M. Cheng, H. C. Hsu, S. L. Chen, W. T. Wu, C. C. Kao, L. J. Lin, et al., "Efficient UV photoluminescence from monodispersed secondary ZnO colloidal spheres synthesized by sol–gel method," J. Cryst. Growth 277, 192 (2005).
[59] M. Eriksson, "Time Resolved Micro Photoluminescence of InGaN/GaN Quantum Dots," Master thesis, Royal Institute of Technology (KTH), (2011).
[60] R. Viter, Z. Balevicius, A. Abou Chaaya, I. Baleviciute, S. Tumenas, L. Mikoliunaite, et al., "The influence of localized plasmons on the optical properties of Au/ZnO nanostructures," J. Mater. Chem. C 3, 6815 (2015).
[61] Y. Zeng, Y. Zhao, and Y. J. Jiang, "Investigation of the photoluminescence properties of Au/ZnO/sapphire and ZnO/Au/sapphire films by experimental study and electromagnetic simulation," J. Alloys Compd. 625, 175 (2015).
[62] K. Saravanan, B. K. Panigrahi, R. Krishnan, and K. G. M. Nair, "Surface plasmon enhanced photoluminescence and Raman scattering of ultra thin ZnO-Au hybrid nanoparticles," J. Appl. Phys. 113, 033512 (2013).
[63] K. Okamoto, I. Niki, A. Scherer, Y. Narukawa, T. Mukai, and Y. Kawakami, "Surface plasmon enhanced spontaneous emission rate of InGaN/GaN quantum wells probed by time-resolved photoluminescence spectroscopy," Appl. Phys. Lett. 87, 071102 (2005).
[64] W. Z. Liu, H. Y. Xu, S. Y. Yan, C. Zhang, L. L. Wang, C. L. Wang, et al., "Effect of SiO2 Spacer-Layer Thickness on Localized Surface Plasmon-Enhanced ZnO Nanorod Array LEDs," ACS Appl. Mater. Interfaces 8, 1653 (2016)
[65] K. Okamoto, I. Niki, A. Shvartser, Y. Narukawa, T. Mukai, and A. Scherer, "Surface-plasmon-enhanced light emitters based on InGaN quantum wells," Nat. Mater. 3, 601 (2004)
[66] W. Z. Liu, H. Y. Xu, L. X. Zhang, C. Zhang, J. G. Ma, J. N. Wang, et al., "Localized surface plasmon-enhanced ultraviolet electroluminescence from n-ZnO/i-ZnO/p-GaN heterojunction light-emitting diodes via optimizing the thickness of MgO spacer layer," Appl. Phys. Lett. 101, 142101 (2012).
[67] Z. Shi, X. Xia, W. Yin, S. Zhang, H. Wang, J. Wang, et al., "Dominant ultraviolet electroluminescence from p-ZnO:As/n-SiC(6H) heterojunction light-emitting diodes," Appl. Phys. Lett. 100, 101112 (2012).
[68] X. M. Mo, H. Long, H. N. Wang, S. Z. Li, Z. Chen, J. W. Wan, et al., "Enhanced ultraviolet electroluminescence and spectral narrowing from ZnO quantum dots/GaN heterojunction diodes by using high-k HfO2 electron blocking layer," Appl. Phys. Lett. 105, 063505 (2014).
[69] H. Wang, Y. Zhao, C. Wu, X. Dong, B. L. Zhang, G. G. Wu, et al., "Ultraviolet electroluminescence from n-ZnO/NiO/p-GaN light-emitting diode fabricated by MOCVD," J. Lumines. 158, 6 (2015).