本論文主要利用調變氧化鋅（ZnO）及二氧化矽（SiO2）含量成分以得到具不同折射率之薄膜，並利用光學模擬軟體（Trace Pro），探討欲增加發光二極體出光之薄膜折射率堆疊設計，並將折射率漸變薄膜層應用於氮化鎵藍色發光二極體表面以改善出光效率。
本實驗採用共濺鍍（co-sputtering）方式濺鍍氧化鋅靶材及二氧化矽靶材，將此方式混合之薄膜（ZnO-SiO¬2 compound thin film）定義為ZnxSiyO3。在薄膜特性部分，ZnO及SiO2兩者皆為透光性極佳之半導體材料，混合濺鍍所得到的ZnxSiyO3薄膜在460nm具有極佳的穿透率（＞90%），且其光吸收邊界隨著Si原子含量增加而有藍移（blue shift）現象，同時ZnxSiyO3薄膜之折射亦隨著下降，其折射率的變動幅度介於ZnO（n~2.1）與SiO2（n~1.46）之間。
在發光二極體之應用上，將ZnxSiyO3薄膜以兩層漸變及三層漸變的堆疊方式，成長於具網狀透明導電膜ITO（mesh-ITO）結構的氮化鎵藍色發光二極體表面。於電流20mA注入下，其順向偏壓（forward voltage）為3.17V與3.19V，比起plane-ITO 3.06V高出約0.1V，而光輸出功率可由4.73mW提升至5.19mW及5.31mW，提高光輸出功率達9.6%及12.2%。並從模擬結果可發現當堆疊層數越高則出光效率越佳。

In this study, we prepared the different refractive index of ZnO-SiO2 compound thin films by changing the contents of ZnO and SiO¬2. First, we used ray-tracing simulation to study the light extraction efficiency of graded-index films stacked on GaN-based LEDs. And then, we implemented the similar structures on GaN-based LEDs to improve the light output power efficiency.
In this experiment, ZnO-SiO2 compound thin films were prepared by co-sputtering, and these kind of compound thin films are defined as ZnxSiyO3. The co-sputtering ZnxSiyO3 thin films indicated high transmittance over 90% around 460nm. The cut-off wavelength of ZnxSiyO3 thin films have blue shift with the Si content increased. Meanwhile, the refractive index was on the decrease. Therefore, the refractive index of ZnxSiyO3 could be varied between 1.46 for pure SiO2 to 2.1 for pure ZnO.
We have demonstrated graded-index ZnxSiyO3 thin films on p-type GaN-based LEDs. The 20mA-forward voltage was varied from 3.06V to 3.17V and 3.19V for LED with plane-ITO, LEDs with two layers and three layers graded-index film inside the circle-hole mesh mesh-ITO, respectively. The 20mA-output power were 4.73mW, 5.19mW and 5.31mW for LED with plane-ITO, LEDs with two layers and three layers graded-index film inside circle mesh-ITO. As our experimental results, we could understand the loss elimination between two layers could be achieved by graded-index thin film.

[1]T. Mukai, M. Yamada, and S. Nakamura, Jpn. J. Appl.Phys 138, 3976 (1999).
[2]Kevin Linthicum, Thomas Gehrke, Darren Thomson, Eric Carlson, Pradeep Rajagopal , Appl. Phys. Lett.75, 1961999).
[3]T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nak-amura,Appl. Phys. Lett. 84, 855(2004).
[4]Chul Huh, Kug-Seung Lee, Eun-Jeong Kang, and Seong-Ju Park, J. App.Phys. 93, 9383, (2003).
[5]http://www.cree.com/ftp/pub/CPR3CM.pdf, High Power Blue LED chips(SiC substrate) have a geometrically enhanced Epi-down design tomaximize light extraction efficiency, and require only a single wire bond78connection.
[6]J. J. Wierer, D. A. Steigerwald, M. R. Krames, J. J. O'Shea, M. J. Ludowise, Appl. Phys.Lett. 78, 3379(2001).
[7]M.Koike, N.Koide, S. Asami, J. Umezaki,in Proc. SPIE Internat-ionalSociety for Optical-Engineering, vol. 3002, pp. 36–39, (1997).
[8]E.F. Schubert, J. K. Kim, and J.-Q. Xi,” Low-refractive-index materials:A new class of optical thin-film materials”, phys. stat. sol. (b) 244, No. 8, 3002–3008(2007).
[9]Jong Kyu Kim, Sameer Chhajed, Martin F. Schubert, E. Fred Schubert, Arthur J. Fischer,Mary H. Crawford, Jaehee Cho, Hyunsoo Kim, and Cheolsoo Sone,” Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact”, Adv. Mater, 20, 801–804(2008).
[10]Jong Kyu Kim, Ahmed N. Noemaun, Frank W. Mont, David Meyaard,E.Fred Schubert,”Elimination of total internal reflection in GaInN light-emitting diodes by graded-refractive-index micropillars”, Appl. Phys.Lett., vol. 93, 221111(2008).
[11]Q. X. Yu, B. Xu, Q. H. Wu, Y. Liao, G. Z. Wang, and R. C. Fang, Appl. Phys. Lett. 83, 4713 (2003).
[12]Z. K. Tang, G. K. L. Wong, P. Yu, M. Kawasaki, A. Ohtomo, H. Koinuma, and Y. Segawa,” Room-temperature ultraviolet laser emission from self-assembled ZnO microcrystallite thin films”, Appl. Phys. Lett. 72, 3270(1998).
[13]D. M. Bagnall, Y. F. Chen, Z. Zhu, T. Yao, S. Koyama, M. Y. Shen, and T. Goto,” Optically pumped lasing of ZnO at room temperature”, Appl.Phys. Lett. 70, 2230(1997).
[14]W. S. Hu, Z. G. Liu, R. X. Wu, Y.-F. Chen, W. Ji, T. Yu, and D. Feng,” Preparation of piezoelectric-coefficient modulated multilayer film ZnO/Al2O3 and its ultrahigh frequency resonance”, Appl.Phys. Lett. 71, 548(1997).
[15]Guo, Xin-Li, Choi, Jae-Hyoung, Tabata, Hitoshi, Kawai, Tomoji, ” Fabrication and Optoelectronic Properties of a Transparent ZnO Homostructural Light-Emitting Diode” , Japanese Journal of Applied Physics, Volume 40, Issue 3A, pp. 177 (2001).
[16]K. Matsubara, P. Fons, K. Iwata, A. Yamada, K. Sakurai, H. Tampo and S. Niki,” ZnO transparent conducting films deposited by pulsed laser deposition for solar cell applications”, Thin Solid Films 431-432, pp. 369-372(2003).
[17]T.Minami, H.Sato, H.Nanto and S.Takata, Jpn.J.Appl.Phys. 24, 781(1985).
[18]L.S.Hsu, C.S.Yeh, C.C.Kuo, B.R.Huang, S.Dhar, Journal of Optoelectronics and Advanced Materials 7, 3039 (2005).
[19]Daniel Nilsson, Fredrik Svahn, Urban Wiklund and Sture Hogmark, ”Low-friction carbon-rich carbide coating deposited by co-sputtering”, Wear Volume 254, Issue11,1084-1091(2003).
[20]Jong Kyu Kim, Ahmed N. Noemaun,Frank W. Mont, David Meyaard,E. Fred Schubert, ” Elimination of total internal reflection in GaInN light-emitting diodes by graded-refractive-index micropillars”, Appl. Phys. Lett. 93, 221111 (2008).
[21]吳永企,“射頻離子束濺鍍(TiO2)x(Ta2O5)1-x 混膜之特性＂,國立中央大學光電科學研究所,碩士論文 (2006).
[22]Helmut Dislich and Paul Hinz,” History and principles of the sol-gel process, and some new multicomponent oxide coatings ”, Journal of Non-Crystalline Solids, Volume 48, Issue 1,p.11-16(1982).
[23]H. Rinnert, M. Vergnat,and G. Marchal,” Structure and optical properties of amorphous SiOx thin films prepared by co-evaporation of Si and SiO”, Materials Science and Engineering Volumes 69-70, p.484-488(2000).
[24]R. Al Asmar, S. Juillaguet, M. Ramonda, ” Fabrication and characterization of high quality undoped and Ga2O3-doped ZnO thin films by reactive electron beam co-evaporation technique”, Journal of Crystal Growth,Volume 275, Issues 3-4,p.512-520(2005).
[25]李正中, “薄膜光學與鍍膜技術,” 藝軒圖書出版社, 第五版。
[26]B. N. Chapman, D. Downer, and L. J. M. Guimarães,” Electron effects in sputtering and cosputtering”, J. Appl. Phys. 45, 2115 (1974).
[27]Hecht, Eugene（2001）．Optics，4th，Pearson Education.
[28]郭浩中,賴芳儀,郭守義,”LED原理與應用”, 五南圖書出版社。
[29]Z. L. Pei, C. Sun, M. H. Tan, J. Q. Xiao, D. H. Guan, R.F. Huang and L. S. Wen, J. Appl. Phys. 90, 3432(2001).
[30]茅一超,”以濺鍍法成長ZnO-SiO2與ZnO-SiNx微晶玻璃薄膜之光學特性研究”, 國立交通大學材料科學與工程學系,碩士論文(2006).
[31]彭羽筠, “以貼靶濺鍍法製備含ZnO量子點之SiO2及SiOxNy奈米複合薄膜之光與電性質研究”. 國立交通大學材料科學與工程學系,博士論文(2008).
[32]M. K. Wu, Y. T. Shih, M. J. Chen, “ZnO quantum dots embedded n a SiO2 nanoparticle layer grown by atomic layer deposition”, P hys. Status Solidi RRL 3, No. 2–3, 88–90 (2009).
[33]Sang-Woo Kim, Shizuo Fujita, Shigeo Fujita,” Self-organized ZnO quantum dots on SiO2/Si substrates by metalorganic chemical vapor deposition” Appl. Phys. Lett. 81, 5036 (2002).