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研究生：	楊於錚 Yang, Yu-Chen
論文名稱：	改良型垂直導通氮化鎵發光二極體之研製及特性改善與分析 Fabrication and Characterization of Advanced Vertical-type GaN-based Light-emitting Diodes
指導教授：	許進恭 Sheu, Jinn-Kong
學位類別：	博士 Doctor
系所名稱：	理學院 - 光電科學與工程學系 Department of Photonics
論文出版年：	2013
畢業學年度：	101
語文別：	英文
論文頁數：	127
中文關鍵詞：	發光二極體、氮化鎵、藍寶石基板、垂直式
外文關鍵詞：	Light-emitting Diode, GaN, Sapphire substrate, Vertical type
相關次數：	點閱：76 下載：6
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近年來因應節能風潮，發光二極體的應用已從傳統的指示燈逐漸轉換至背光光源、戶外看板及室內外照明等領域。新的應用範圍所需供應的亮度較高，因此驅動每一顆發光二極體所使用的電流及其輸出的瓦數也較高，實際使用狀態下產生的熱能如何散逸也就成為了一個十分重要的課題。常見的改良方式是選擇將散熱較差的藍寶石基板置換成其他導熱係數較佳的材料作為新的基板，但因使用基板剝離技術容易導致磊晶應力釋放，可能導致漏電流的產生。本論文主要針對垂直導通型的發光二極體之光電特性進行改善，第一部分將會先討論如何改善固有製程中已知的問題點。第二部分我們就光電特性的提升，在此結構上捨棄將藍寶石基板移除的製程，改由研磨及蝕刻製程將n型氮化鎵暴露出來，並保留部分的藍寶石原生基板，不僅可避免因使用基板剝離技術而造成的漏電流，且發光效率還可進一步提升。最後我們因應未來照明趨勢可能會偏向高電壓及高功率操作，設計一款高壓串接式的發光二極體。此種設計組合了數個發光二極體單元於單一基板上，因每一發光二極體單元的尺寸較小，因此電流分布較佳，同時也觀察到個別晶粒均有操作電壓降低及發光效率提升之現象，結合散熱能力佳及高發光效率兩大優勢，更適合作為新一代高功率應用的元件。

In recent years, the applications of light-emitting diodes (LEDs) gradually transit from traditional indicator lamps to backlighting, outdoor billboards, and lighting. New applications need higher brightness, and the input power for these applications is also increased. How to dissipate the heat out from LEDs has become a very important issue. One solution is to use new materials with high coefficient of thermal conductivities to replace the sapphire substrate. But the strain release and laser-induced damage on the GaN-based epitaxial layers led to the degradation of electrical properties of the conventional vertical LEDs. In this dissertation, we will research how to improve the optical and electrical characteristics of vertical InGaN LEDs. The first part focuses on the process improving on vertical InGaN LEDs. The design of the Vertical InGaN LEDs with a retained sapphire will be discussed at the second part. This design can reduce the reverse leakage current (Ir) because there are no strain release and laser-induced damage on the GaN-based epitaxial layers. Also, the top sapphire layer serves as a window layer to facilitate light extraction. At last section, we propose designs of high voltage vertical InGaN LEDs. These designs connect several LED cells on a single substrate in series or parallel. Because the LED cells are smaller than regular ones, they have more uniform distribution of injection current. The characteristics of forward voltages and light extraction efficiencies of high voltage vertical InGaN LEDs are also better than vertical InGaN LEDs with single cell. The multi-cell vertical InGaN LEDs are more suitable for high power applications in the future.

摘要……………………………………………………………………………………………………………………………………………… I
Abstract……………………………………………………………………………………………………………………………………II
致謝………………………………………………………………………………………………………………………………………… III
Contents………………………………………………………………………………………………………………………………… IV
Table Captions……………………………………………………………………………………………………………… VII
Figure Captions………………………………………………………………………………………………………… VIII
Chapter 1  Introduction…………………………………………………………………………………………… 1
1.1	 Recent development of high power InGaN light-emitting diodes………………………………………………………………………………………………………………… 1
1.2	 The advantage of vertical InGaN light-emitting diodes………………………………………………………………………………………………………………………………………… 3
1.3	 Motivation…………………………………………………………………………………………………… 11
References in Chapter 1………………………………………………………………………………………… 12

Chapter 2  Process improving on vertical InGaN light-emitting diodes……………………………………………………………………………………………………………… 14
2.1  The high reflectivity Ohmic contact layer on p-GaN…… 14
2.2  The barrier layer on Ag layer…………………………………………………………… 20
2.3  The encapsulated reflector…………………………………………………………………… 25
2.4  The void-free wafer bonding process…………………………………………… 31
2.4.1  The preparation of samples……………………………………………………………… 32
2.4.2  Results and discussion………………………………………………………………………… 33
References in Chapter 2………………………………………………………………………………………… 40

Chapter 3  Vertical InGaN light-emitting diodes with a sapphire-face-up structure………………………………………………………………………………… 41
3.1  Introduction………………………………………………………………………………………………………… 41
3.2  The preparation of samples…………………………………………………………………… 46
3.3  The retained sapphire substrate……………………………………………………… 49
3.3.1  Sapphire thinning by grinding and polishing………………… 49
3.3.2  Sapphire etching by inductively coupled plasma (ICP)……………………………………………………………………………………………………………………………………………………… 51
3.4  Comparison of optical and electrical characteristics between VLEDs with and without retained sapphire……………………… 59
3.5  Sapphire surface texturing…………………………………………………………………… 69
3.5.1  Formation of metal nanomask…………………………………………………………… 69
3.5.2  Sapphire surface texturing by ICP dry etching…………… 70
3.6  The VLEDs with retained patterned sapphire substrate……………………………………………………………………………………………………………………………… 77
3.6.1  The morphology of exposed GaN layer……………………………………… 77
3.7  Comparison of optical and electrical characteristics between VLEDs with and without retained patterned sapphire………………………………………………………………………………………………………………………………… 81
3.8  The light output efficiency simulation for difference sapphire thickness……………………………………………………………………………………………………… 90
3.9  Comparison between vertical InGaN light-emitting diodes with retained patterned sapphire and the flip-type InGaN light-emitting diodes……………………………………………………………………………………………… 95
3.9.1  The conventional InGaN flip-chip……………………………………………… 95
3.9.2  The advanced InGaN flip-chip………………………………………………………… 96
3.10  Results and discussion………………………………………………………………………… 102
References in Chapter 3……………………………………………………………………………………… 103

Chapter 4  The multi-cell vertical InGaN light-emitting diodes…………………………………………………………………………………………………………………………………… 107
4.1  The efficiency improving limitations on vertical single-cell InGaN light-emitting diodes…………………………………………… 107
4.2  High voltage design of vertical multi-cell InGaN light-emitting diodes…………………………………………………………………………………………………………… 108
4.3  The preparation of samples………………………………………………………………… 111
4.4  Comparison of optical and electrical characteristics between single-cell and multi-cell VLEDs………………………………………… 115
4.4.1  Current spreading analysis with near field measurement……………………………………………………………………………………………………………………… 116
4.5  Results and discussion…………………………………………………………………………… 123
References in Chapter 4……………………………………………………………………………………… 124

Chapter 5  Conclusions and future works…………………………………………… 125
5.1  Conclusions………………………………………………………………………………………………………… 125
5.2  Future works……………………………………………………………………………………………………… 126

Publication List………………………………………………………………………………………………………… 127


                                    

References in Chapter 1
[1] S. Nakamura, “InGaN/AlGaN blue-light-emitting diodes”, J. Vac. Sci. & Tech. A. vol 13, no. 3, pp. 705-710, 1995.
[2] A. Chakraborty, B.A. Haskell, S. Keller, J.S. Speck, S.P. DenBaars, S. Nakamura, U.K. Mishra, “Nonpolar InGaN/GaN emitters on reduced-defect lateral epitaxially overgrown a-plane GaN with drive-currentindependent electroluminescence emission peak”, Appl. Phys. Lett., vol.85, no. 22, pp. 5143-5145, 2005.
[3] H. Zhong, A. Tyagi, N. Fellows, F. Wu, R. Chung, M. Saito, K. Fujito, J. Speck, S. DenBaars, S. Nakamura, “High power and high efficiency blue light emitting diode on freestanding semipolar (10 ) bulk GaN substrate”, Appl. Phys. Lett., vol. 90, 233504, 2007.
[4] A. Dadgar, A. Alam, T. Riemann, J. Blasing, A. Diez, M. Poschenrieder, M. Straßburg, J. Christen, and A. Krost, “Crack-Free InGaN/GaN Light Emitters on Si(111)”, Phys. Status Solidi A., vol. 188, pp. 155-158, 2001.
[5] A. Dadgar, M. Poschenrieder, J. Blasing, K. Fehse, A. Diez, and A. Krost, “Thick, crack-free blue light-emitting diodes on Si(111) using low-temperature AlN interlayers and in situ SixNy masking”, Appl. Phys. Lett., vol. 80, pp. 3670-3672, 2002.
[6] M. R. Krames, G. E. Höfler, E. I. Chen, I. H. Tan, P. Grillot, N. F. Gardner, H. C. Chui, J. W. Huang, S. A. Stockman, F. A. Kish, and M. G. Craford, “High power truncated inverted pyramid AlxGa12x.0.5In0.5P/GaP light-emitting diodes exhibiting >50% external quantum efficiency,” Appl. Phys. Lett., vol. 75, pp. 2365-2367, 1999.
[7] T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening”, Appl. Phys. Lett., vol. 84, no. 6, pp. 855-857, 2004.
[8] H. W. Huang, J. T. Chu, C. C. Kao, T. H. Hseuh, T. C. Lu, H. C. Kuo, S. C. Wang, and C. C. Yu, “Enhanced light output of an InGaN/GaN light emitting diode with a nano-roughened p-GaN surface”, Nanotechnology, vol. 16, pp. 1844-1848, 2005.
[9] D. S. Kuo, S. J. Chang, T. K. Ko, C. F. Shen, S. J. Hon, and S. C. Hung, “Nitride-based LEDs with phosphoric acid etched undercut sidewalls,” IEEE Photon. Technol. Lett., vol. 21, no.8, pp. 510-512, 2009.
[10] K. McGroddy, A. David, E. Matioli, M. Iza, S. Nakamura, S. DenBaars, J. S. Speck, C. Weisbuch, and E. L. Hu, “Directional emission control and increased light extraction in GaN photonic crystal light emitting diodes”, Appl. Phys. Lett., vol. 93, 103502, 2008.

References in Chapter 2
[1] T. Mori, T. Kozawa, T. Ohwaki, Y. Taga, S. Nagal, S. Yamasaki, S. Asami, N. Shibata, M. Koide, “Schottky Barriers and Contact Resistances on p-type GaN”, Appl. Phys. Lett., vol. 69, pp. 3537-3539, 1996.
[2] J. O. Song, J. S. Kwak, Y. J. Park, and T. Y. Seong, “Ohmic and degradation mechanisms of Ag contacts on p- type GaN,” Appl. Phys. Lett., vol. 86, 062104, 2005.
[3] F. Jiang, L.E. Cai, J.Y. Zhang, B.P. Zhang, “Formation of high reflective Ni/Ag/Ti/Au contact on p-GaN,” Physica E, vol. 42, pp. 2420-2423, 2010.
[4] J. S. Jang, S. J. Park, and T. Y. Seong, “Metallization scheme for highly low-resistance, transparent, and thermally stable ohmic contacts to p-GaN,” Appl. Phys. Lett., vol. 76, pp. 2898-2900, 2000.
[5] W. S. Wong, M. Kneissl, P. Mei, D. W. Treat, M. Teepe and N. M. Johnson, “Continuous-wave InGaN multiple-quantum-well laser diodes on copper substrates,” Appl. Phys. Lett., vol. 78, pp. 1198-1200, 2001.
[6] S. C. Hsu and C. Y. Liu, “Fabrication of Thin-GaN LED Structures by Au–Si Wafer Bonding,” Electrochemical and Solid-State Letters, vol. 9, G171-G173, 2006.
[7] D. S. Wuu, S. C. Hsu, S. H. Huang, C. C. Wu, C. E. Lee and R. H. Horng, “GaN/Mirror/Si Light-Emitting Diodes for Vertical Current Injection by Laser Lift-Off and Wafer Bonding Techniques,” Jpn. J. Appl. Phys., vol. 43, pp. 5239-5242, 2004.
[8] R. H. Horng, Y. C. Lien, W. C. Peng, D. S. Wuu, C. Y. Tseng, C. H. Seieh, M. F. Huang, S. J. Tsai and J. S. Liu, “High-Brightness Wafer-Bonded Indium-Tin Oxide/Light-Emitting Diode/Mirror/Si,” Jpn. J. Appl. Phys., vol. 40, pp. 2747-2751, 2001.
[9] S. J. Kim, J. H. Jang, and J. S. Lee, “Thermally Stable and Highly Reflective ITO/Ag-Based Ohmic Contacts to p-GaN,” J. Electrochem. Soc., vol. 154, pp. H973-H976, 2007.

References in Chapter 3
[1] E. F. Schubert, Light-emitting diode, 2nd ed. Cambridge: Cambridge University Press, 2006, pp. 150-160.
[2] W. S. Wong, M. Kneissl, P. Mei, D. W. Treat, M. Teepe, and N. M. Johnson, “Continuous-wave InGaN multiple-quantum-well laser diodes on copper substrates,” Appl. Phys. Lett., vol. 78, no.9, pp. 1198-1200, 2001.
[3] S. C. Hsu, B. J. Pong, W. H. Li, E. T. Beechem, S. Graham, and C. Y. Liu, “Stress relaxation in GaN by transfer bonding on Si substrates,” Appl. Phys. Lett., vol. 91, no. 25, 251114, 2007.
[4] D. S. Wuu, S. C. Hsu, S. H. Huang, C. C. Wu, C. E. Lee, and R. H. Horng, “GaN/mirror/Si light-emitting diodes for vertical current injection by laser lift-off and wafer bonding techniques,” Jpn. J. Appl. Phys., vol. 43, pp. 5239-5242, 2004.
[5] M. K. Kelly, O. Ambacher, B. Dahlheimer, G. Groos, R. Dimitrov, H. Angerer, and M. Stutzmann, “Optical patterning of GaN films,” Appl. Phys. Lett., vol. 69, pp. 1749-1751, 1996.
[6] W. S. Wong, T. Sands, and N. W. Cheung, “Damage-free separation of GaN thin films from sapphire substrates,” Appl. Phys. Lett., vol. 72, pp. 599-601, 1998.
[7] Y. C. Sermon Wu, J. H. Cheng, W. C. Peng, and H. Ouyang, “Effects of laser sources on the reverse-bias leakages of laser lift-off GaN-based light-emitting diodes,” Appl. Phys. Lett., vol. 90, 251110, 2007.
[8] S. H. Huang, R. H. Horng, S. C. Hsu, T. Y. Chen, and D. S. Wuu, “Surface texturing for wafer-bonded vertical-type GaN/mirror/Si light-emitting diodes,” Jpn. J. Appl. Phys., vol. 44, pp. 3028-3031, 2005.
[9] C. M. Tsai, J. K. Sheu, W. C. Lai, M. L. Lee, S. J. Chang, C. S. Chang, T. K. Ko, and C. F. Shen, “GaN-based LEDs output power improved by textured GaN/sapphire interface using in situ SiH4 treatment process during epitaxial growth,” IEEE J. Sel. Top. Quantum Electron., vol. 15, pp. 1275-1280, 2009.
[10] Lester; Steven D. (Palo Alto, CA), Steigerwald; Daniel A. (Cupertino, CA), and Wierer, Jr.; Jonathan J. (Fremont, CA), Lumileds Lighting, U.S., LLC (San Jose, CA), “Highly reflective ohmic contacts to III-nitride flip-chip LEDs,” U.S. Pat. 6573537, 2003.
[11] D. L. Hibbard, S. P. Jung, C. Wang, D. Ullery, Y. S. Zhao, H. P. Lee, W. So, and H. Liu, “Low resistance high reflectance contacts to p-GaN using oxidized Ni/Au and Al or Ag,” Appl. Phys. Lett., vol. 83, pp. 311-313, 2003.
[12] C. H. Lee, Y. M. Wong, C. Doherty, K. L. Tai, E. Lane, D. D. Bacon, F. Baiocchi, and A. Katz, “Study of Ni as a barrier metal in AuSn soldering application for laser chip/submount assembly,” J. Appl. Phys., vol. 72, pp. 3808-3815, 1992.
[13] Carter-Coman; Carrie (San Jose, CA), Hofler; Gloria (Sunnyvale, CA), and Kish, Jr.; Fred A. (San Jose, CA), LumiLeds Lighting, U.S. LLC (San Jose, CA), “Diffusion barrier for increased mirror reflectivity in reflective solderable contacts on high power LED chip,” U.S. Pat. 6222207, 2003.
[14] Tsau, C. H., Spearing, S. M., Schmidt, M. A., “Characterization of wafer-level thermocompression bonds,” J. Microelectromech. Syst., vol. 13, pp. 963-971, 2004.
[15] D. S. Wuu, W. K. Wang, K. S. Wen, S. C. Huang, S. H. Lin, R. H. Horng, Y. S. Yu, and M. H. Pan, “Fabrication of pyramidal patterned sapphire substrates for high-efficiency InGaN-based light emitting diodes,” J. Electrochem. Soc., vol. 153, pp. G765-G770, 2006.
[16] J. Wang, L. W. Guo, H. Q. Jia, Y. Wang, Z. G. Xing, W. Li, H. Chen, J. M. Zhou, “Fabrication of patterned sapphire substrate by wet chemical etching for maskless lateral overgrowth of GaN,” J. Electrochem. Soc., vol. 153, pp. C182-C185, 2006.
[17] M. E. Lin, Z. F. Fan, Z. Ma, L. H. Allen, and H. Morkoq, “Reactive ion etching of GaN using BCl3,” Appl. Phys. Lett., vol. 64, pp. 887-888, 1994.
[18] Y. J. Sung, H. S. Kim, Y. H. Lee, J. W. Lee, S. H. Chae, Y. J. Park, and G. Y. Yeom, “High rate etching of sapphire wafer using Cl2/BCl3/Ar inductively coupled plasmas,” Mater. Sci. Eng. B, vol. 82, pp. 50-52, 2001.
[19] C. H. Jeong, D. W. Kim, J. W. Bae, Y. J. Sung, J. S. Kwak, Y. J. Park , and G. Y. Yeom, “Dry etching of sapphire substrate for device separation in chlorine based inductively coupled plasmas,” Mater. Sci. Eng. B, vol. 93, pp. 60-63, 2002.
[20] D. W. Kim, C. H. Jeong, K. N. Kim, H. Y. Lee, H. S. Kim, Y. J. Sung, and G. Y. Yeom, “High rate sapphire (Al2O3) etching in inductively coupled plasmas using axial external magnetic field,” Thin Solid Films, vol. 435, pp. 242-246, 2003.
[21] H. Y. Kuo, S. J. Wang, P. R. Wang, K. M. Uang, T. M. Chen, S. L. Chen, W. C. Lee, H. K. Hsu, J. C. Chou, and C. H. Wu, “Use of elastic conductive adhesive as the bonding agent for the fabrication of vertical structure GaN-based LEDs on flexible metal substrate,” IEEE Photon. Technol. Lett., vol. 20, pp. 523-525, 2008.
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References in Chapter 4
[1] A. Keppens, W. R. Ryckaert, G. Deconinck, and P. Hanselaer, “High power light-emitting diode junction temperature determination from current–voltage characteristics,” J. Appl. Phys., vol. 104, 093104, 2008.
[2] X. Guo and EF Schubert, “Current crowding in GaN/InGaN light emitting diodes on insulating substrates,” J. Appl. Phys., vol. 90, pp. 4191-4195, 2001.
[3] Y. C. Shen, G. O. Mueller, S. Watanabe, N. F. Gardner, A. Munkholm, and M. R. Krames, “Auger recombination in InGaN measured by photoluminescence,” Appl. Phys. Lett., vol. 91, 141101, 2007.
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[5] Y. Y. Kudryk and A. V. Zinovchuk, “Efficiency droop in InGaN/GaN multiple quantum well light-emitting diodes with nonuniform current spreading,” Semicond. Sci. Technol., vol. 26, 095007, 2011.
[6] C. K. Li and Y. R. Wu, “Current spreading effect in vertical GaN/InGaN LEDs,” Proc. SPIE, vol. 7939, 79392K, 2011.
[7] C. K. Li and Y. R. Wu, “Study on the current spreading effect and light extraction enhancement of vertical GaN/InGaN LEDs,” IEEE Trans. Electron Device, vol. 59, no. 2, pp. 400-407, 2012.

校內：2018-08-07公開
校外：2018-08-07公開

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