為提升GaN-LED之亮度及發光功率，目前相關研發工作皆正朝著高功率大面積發展。移除藍寶石基板之垂直結構GaN-LED雖已研製成功，實驗結果亦顯示光電特性之大幅度改善，然由於p-GaN無法高濃度摻雜，其導電率不佳，電流均勻分佈尚未臻理想。藉由沉積一層透明導電層(Transparent Conducting Layer, TCL)於GaN磊晶層表面以及適當之電極及元件結構設計，將可以有效改善電流分佈增加發光效率。
　　本論文旨在針對垂直結構大面積GaN-LED之電極設計進行二維電性模擬分析，深入探討電極圖案設計及不同透明導電層結構對GaN-LED之電流分佈及光電特性之影響。研究結果發現GaN磊晶層表面形變結合透明導電層，對於LED電流均勻分佈之影響極為顯著。為有效改善電流均勻分佈，本論文提出數種可以之電極圖案設計及新穎表面磊晶層非等向性蝕刻之垂直結構GaN-LED，並就相關模擬結果進行分析與討論。

　　Recently, there are increasing interests in promoting the optoelectronic optical-electrical performance and light output power of GaN-based light emitting diodes (LEDs). Though vertical-structured GaN-based LEDs, which have been shown having a much better performance as compared to conventional lateral-structured LEDs, have been successfully developed employing laser liff-off (LLO) technology to remove the insulating sapphire substrate, insufficient doping concentration in p-GaN usually results in a poor current spreading and nonuniform light emission. Under the circumstances, the deposition of a Transparent Conducting Layer (TCL) and a contact electrode with a well-designed geometry are very necessary, especially for large-area and high power LEDs.
　　In this thesis, attempts were made for the geometry design of large area high power GaN-LEDs. ISE-TCAD was used for the theoretical calculations of optoelectronic performances of devices with various contact geometry and TCL design. Based on the simulation results, several contact geometrical designs in conjunction with a suitable TCL favored for uniform distributions of current and light emission were proposed. To further improve the uniformity of light emission, a novel method using an anisotropic etching to the top n-GaN layer of the GaN-LED was also proposed. Simulation results with an emphasis on etching depth and contour as well as related discussions were made.

[1]　史光國“現代半導體發光及雷射二極體材料技術”全華科技圖書
[2]　A. Zukauskas, M. S. Shur, and R. Gaska, Introduction to Solid-State Lighting. New York: Wiley, 2002.
[3]　S. Nakamura and S. F. Chichibu, Introduction to Nitride Semiconductor Blue Laser Diode and Light Emitters Diodes. London, U.K.: Taylor and Francis,2000.
[4]　Semiconductor Physics & Devices,Third Edition.Author: Donald A.Neamen
[5]　工業材料，1998/6月，P140
[6]　www.compoundsemiconductor.net
[7]　www.digitimes.com.tw
[8]　www.cree.com
[9]　Shui-Jinn Wang, Tron-Min Chen, Kai-Ming Uang, Shiue-Lung Chen1, Ching-Chung Tsai1, Bor-Wen Liou and Su-Hua Yang “Use of Anisotropic Laser Etching and Transparent Conducting Layer to Alleviate Current Crowding Effect in Vertical-Structured GaN-Based Light-Emitting Diodes,” Device Researh conference June 2006
[10]　E.F.Schubert, Light-emitting Diode (CambridgeUniversityPress, Cam-bridge, UK, 2003)
[11]　C. F. Chu, C. C. Yu, H. C. Cheng, C. F. Lin, and S. C. Wang,“Comparison of p-side down and p-side up GaN light-emitting diodes fabricated by laser lift-off,”Jpn. J. Appl. Phys., vol. 42, pp.L147–L150, Feb. 2003.
[12]　S. Nakamura, N. Iwasa, M. Senoh, and T. Mukai,“Hole Compensation Mechanism of p-Type GaN Films,”Jpn. J. Appl. Phys., vol. 31, p.1258, 1992.
[13]　Abhishek Motayed, Ravi Bathe, Mark C. Wood, Ousmane S. Diouf, R. D. Vispute, and S. Noor Mohammad,“Electrical, thermal, and microstructural characteristics of Ti/Al/Ti/Au multilayer Ohmic contacts to n-type GaN,”J. Appl. Phys., vol. 93, p. 1087, 2003.
[14]　W. Y. Lin, D. S. Wuu, K. F. Pan, S. H. Huang, “High-Power GaN–Mirror–Cu Light-Emitting Diodes for Vertical Current Injection Using Laser Liftoff and Electroplating Techniques,”IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 17, NO. 9, SEPTEMBER 2005.
[15]　Shui-Jinn Wang', Shiue-Lung Chen', Kai-Ming Uang' , Yu-Cheng Yang,Tron-Min Chen', and Bor-Wen Liou,“Effect of Surface Treatment on the performances of Vertical-structuredGaN-based LEDs with Electroplating Metallic Substrate,”IEEE 2005
[16]　Dong-Sing WUU(武東星)“Progress in vertical GaN/ mirror/ Si Blue LEDs,”2003 Taiwan-Japan Optoelectronic WorkShop
[17]　Hunsang Kim, Ji-Myon Lee, Chul Hun “Modeling of GaN–based ligt–emitting dode for uniform current spreding,”Appl. Phys. Lett., Vol. 77, No. 12, 18 September 2000
[18]　D.w.kin, H. Y. lee, and G.Y. Yeom “A study of transparent contact to vertical GaN-based light-emitting diodes,” J.Appl.phs.,vol 98,p.3102,2005
[19]　DEVISE, Release 10.0, ISE AG,Zurich,2005
[20]　MDRAW, Relesse 10.0, ISE AG,Zurich,200
[21]　DESSIS, Relesse 10.0, ISE AG,Zurich,2005
[22]　Semiconductor Physics & Devices, Third Edition . Author: Donald A. Neamen