為改善氮化鎵發光二極體(GaN Light-Emitting Diode)的電流分佈，以得到高發光效率的元件，一直以來都被視為研究重點。如使用藍寶石基板(Sapphire)作為發光二極體元件基板，因藍寶石基板並不導電，必須使p型與n型電極位於同一面，導致電流從p型電極橫向流至n型電極時，容易產生電流擁擠現象，影響發光效率。經霍爾量測可知，p型氮化鎵的片電阻遠大於n型氮化鎵與ITO透明導電層，因此電流可視為在n型氮化鎵層與ITO透明導電層兩層之間做競爭。
本實驗主要為鍍製電流阻擋層與改變透明導電層材料與厚度來製作發光二極體元件，藉由改變電流分佈來影響發光效率，最後量測並比較各元件之I-V及L-I曲線，同時觀察不同厚度之透明導電層發光情形，以了解不同元件之電流擴散長度與其影響。
在鍍製p型電極前，可明顯看到電流阻擋層的效果，其發光功率比無電流阻擋層元件提升了25%。另外增加透明導電層厚度或降低其電阻率，可使透明導電層片電阻值越小，電流擴散長度越長，接觸電阻越小，發光面積越大。

To produce higher light-output power by improving non-uniform current distribution of GaN light emitting diodes (LED) has been one of the major endeavors in LED industry. When a sapphire substrate is used as a LED substrate, p-type and n-type electrodes should be located on the same side of the chip because the sapphire substrate does not conduct electricity. As a result, the current tends to crowd as it flows laterally from p-type electrode to n-type electrode, which affects light quantum efficiency. From Hall measurement, we know p-GaN sheet resistance is much larger than n-GaN and ITO transparent conductive layer(TCL), so the current flow is divided between n-type GaN layer and the ITO transparent conductive layer.
In this study, the researcher used current blocking layer(CBL) and different TCL material and thicknesses to produce light-emitting diodes. And by changing the current distribution, the light output power was changed. The researcher measured and compared I-V and L-I curves of various devices and recorded their illumination distribution to characterize their current spreading lengths and the effects.
Before adding p-pad electrode, we clearly observed the effect of current blocking layer, the light output power compared to LED without CBL was improved by 25%. In addition, by increasing the thickness or decreasing the resistivity of transparent conductive layer, the sheet resistance became smaller and thus the current spreading length was increased, the contact resistance was reduced, and the illumination area was increased.

[1] T. Matsuoka, H. Okamoto, M. Nakao, H. Harima, E. Kurimoto, “Optical bandgap energy of wurtzite InN,” Appl. Phys. Lett., Vol. 81, No. 3, pp. 1246-1248 (2002)

[2] V. Y. Davydov, A. A. Klochikhin, V. V. Emtsev , F. Bechstedt , A.V. Mudryi, E. E. Halle, “Absorptionand Emission of Hexagonal InN. Evidence of Narrow Fundamental Band Gap,” Physica Status Solidi, B Vol. 229, No. 3, pp. R1~R3 (2002)

[3] H. J. Round “A note on carborundum ,” Electrical World, Vol. 49, No. 6, p. 309 (1907)

[4] O. V. Lossev , “Luminous carborundum detector and detection effect and oscillations with crystals,” Phil. Mag., Vol. 6, pp. 1024-1044, 1928.

[5] R. M. Potter, J. M. Brank and A. Addamiano “Silicon carbide light-emitting diodes,” J. Appl. Phys., Vol. 40, No. 5 , pp. 2253-2257 (1969)

[6] G. Destriau, “AC electroluminescence in ZnS ”, J. Chimie Phys., vol.33, p.587 (1936)

[7] H. Welker, “On new semiconducting compounds,” Zeitschrift fur
Naturforschung A (Astrophys., Phys. Physikal. Chem.), vol. 7a, pp.
744–749, Nov. (1952)

[8] H. Welker, “On new semiconducting compounds. II,” Zeitschrift fur
Naturforschung A (Astrophys., Phys. Physikal. Chem.), vol. 8a, pp.
248–251, Nov. (1953)

[9] N. Holonyak, Jr. and S. F. Bevacqua, “Coherent (visible) light emission from Ga(AsP) junctions,” Appl. Phys. Lett., vol. 1, pp. 82–83, Dec. 1 (1962)

[10] Johnson, W. C., Parsons, J. B., Crew, J. Phys. Chem., Vol. 36, p. 2561 (1932)

[11] Maruska, H. P. and Tietjen, The preparation and properties of vapor-deposited single-crystalline GaN. Appl. Phys. Lett., Vol. 15, p. 327. (1969)

[12] Pankove, J. I., Miller E. A. and Berkeyheiser, GaN Electroluminescence Diodes. RCA Review, Vol. 32, p. 383 (1971)

[13] H. P. Maruska, W. C. Rhines, and D. A. Stevenson, “Preparation of Mg-doped GaN diodes exhibiting violet electroluminescence,” Mat. Res. Bull., Vol. 7, pp. 777-781 (1972)

[14] H. Amano, M. Kito, K. Hiramatsu, and I. Akasaki, "P-Type Conduction in Mg-Doped GaN Treated with Low-Energy Electron-Beam Irradiation," Japanese Journal of Applied Physics Part 2-Letters, vol. 28, pp. L2112-L2114 (1989)

[15] S.Yoshida, S. Misawa, S. Gonda, "Epitaxial growth of GaN/AlN heterostructures, " J. Vac. Sci. Technol. B 1, 250 (1983)

[16] 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)

[17] 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)

[18] 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)

[19] H. Amano, M. Kito, K. Hiramatsu, and I. Akasaki, Jpn. J. Appl. Phys. 28, L2112 (1989).

[20] S. Nakamura and G. Fasol, “The Blue Laser Diode, ” Berlin, Springer, (1997)

[21] 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)

[22] S. Nakamura, M. Senoh, N. Iwasa and S. Nagahama “High-brightness InGaN blue, green, and yellow lightemitting diodes with quantum well structures,” Jpn. J. Appl. Phys., Vol. 34, pp. L797-L799 (1995)

[23] S. Nakamura, M. Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, Y. Sugimoto, and H. Kiyoku, “Room-temperature continuous-wave operation of InGaN multi-quantum-well structure laser diodes,” Appl. Phys. Lett., Vol. 69, No. 26, pp.4056-5408 (1996)

[24] R. D. Dupuis, and M. R. Krames, “History, Development, and Applications of High-Brightness Visible Light-Emitting Diodes,” Journal of Lightwave Technology, Vol. 26, No. 9, pp.1154-1171 (2008)

[25] C. Kittel, Introduction to Solid State Physics , (John Wiley Press), Chap.8. (1996)

[26] E. Fred Schubert, “Light-emitting diode,” Cambridge University Press (2003)

[27] Katsushi Akita, Takashi Kyono, Yusuke Yoshizumi, Hiroyuki Kitabayashi, and Koji Katayama, “Improvements of external quantum efficiency of InGaN-based blue light-emitting diodes at high current density using GaN substrates.” J. Appl. Phys. 101, 033104 (2007)

[28] Lumileds Lighting, http://www.lumileds.com.

[29] M. R. Krames, M. Ochiai-Holcomb, G. E. Hofler, C. Carter-Coman,
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 pyramid (Al0.5Ga1-x)0.5In0.5P/GaP light emitting diodes exhibiting >50% external quantum efficiency,” Appl. Phys. Lett. 75, 2365 (1999)

[30] 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)

[31] H. Sugawara, M. Ishikawa, and G. Hatakoshi, “High-efficiency InGaAlP/GaAs visible light-emitting diodes,” Appl. Phys. Lett., Vol. 58, pp. 1010-1012 (1991)

[32] S. Grzanka, G. Franssen, G. Targowski, K. Krowicki, T. Suski, R. Czernecki, P. Perlin, and M. Leszczyński, “Role of the electron blocking layer in the low-temperature collapse of electroluminescence in nitride light-emitting diodes,” Appl. Phys. Lett., Vol. 90, pp. 103507 (2007)

[33] Strategies in light ( 2003)

[34] 郭浩中, 賴芳儀 , 郭守義, LED原理與應用 ( 2009)

[35] NICHIA Corporation, http://www.nichia.co.jp

[36] M. Y. Hsieh, C. Y. Wang, L. Y. Chen, T. P. Lin, M. Y. Ke, Y. W. Cheng, Y. C. Yu, C. P. Chen, D. M. Yeh, C. F. Lu, C. F. Huang, C. C. Yang, and J. J. Huang, “Improvement of External extractionefficiency in GaN-based LEDs by SiO2 nanosphere lithography,” IEEE Electron Device Lett., Vol. 29, pp. 658-660, (2009)

[37] D. A. Stocker, E. F. Schubert, and J. M. Redwing, “Crystallographic wet chemical etching of GaN,” Appl. Phys. Lett., Vol. 73, No. 18, pp. 2654-2656, (1998)

[38] 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. 855-858 (2004)

[39] E. Fred Schubert, “Light-emitting diode,” Cambridge University Press, second edition(2th) (2003)
[40] C. J. Nuese, J. J. Tietjen, J. J. Gannon, and H. F. Gossenberger, “Optimization of electroluminescent efficiencies for vapor-grown GaAsP diodes,” J. Electrochem. Soc., Vol. 116, pp. 248-253 (1969)

[41] W. O. Groves and A. S. Epstein, “Epitaxial deposition of III–V compounds containing isoelectronic impurities,” US Patent 4,001,056 (1977)

[42] C. P. Kuo, R. M. Fletcher, T. D. Osentowski, M. C. Lardizabal, M. G. Craford, and V. M. Robbins, “High performance AlGaInP visible light-emitting diodes,” Appl. Phys. Lett., Vol. 57, pp. 2937-2939 (1990)

[43] H. Sugawara, M. Ishikawa, and G. Hatakoshi, “High-efficiency InGaAlP/GaAs visible light-emitting diodes,” Appl. Phys. Lett., Vol. 58, pp. 1010-1012 (1991)

[44] H. Sugawara, K. Itaya, H. Nozaki, and G. Hatakoshi, “High-brightness InGaAlP green light-emitting diodes,” Appl. Phys. Lett., Vol. 61, pp. 1775-1777 (1992)

[45] C. D. Moyer, “Photon recycling light emitting diode,” US Patent 4,775,876 (1988)

[46] J. Nishizawa, M. Koike and C. C. Jin, “Efficiency of GaAlAs heterostructure red light-emitting diodes,” J. Appl. Phys., Vol. 54, pp.2807-2812 (1983)

[47] S. Y. Kim, H. W. Jang, and J.-L. Lee, “High-brightness GaN-based light-emitting diode with indium tin oxide based transparent ohmic contact, ” J. Vac. Sci. Technol. B, Vol. 22, pp. 1851-1857 (2004)

[48] H. Kim, S. J. Park, H. Hwang, and N. M. Park, “Lateral current transport path, a model for GaN-based light-emitting diodes: Applications to practical device designs,” Appl. Phys. Lett., Vol. 81, pp. 1326-1328 (2002)

[49] M. Rattier, H. Benisty, R. P. Stanley, J-F Carlin, R. Houdré, U. Oesterle, C. J. M. Smith, C. Weisbuch, and T. F. Krauss “Toward Ultrahigh-Efficiency Aluminum Oxide Microcavity Light-Emitting Diodes: Guided Mode Extraction by Photonic Crystals,” IEEE J Sel Top Quantum Electron, Vol. 8, pp. 238-247( 2002)

[50] W. B. Joyce and S. H. Wemple, “Steady-State Junction-Current Distributions in Thin Resistive Films on Semiconductor Junctions,” Journal of Applied Physics, Vol. 41, No. 9, pp. 3818-3830 (1970)

[51] H. Kim, J. M. Lee, C. Huh, S. W. Kim, D. J. Kim, S. J. Park, and Hyunsang Hwang, “Modeling of a GaN-based light-emitting diode for uniform current spreading,” Appl. Phys. Lett., Vol.77, pp. 1903-1904, (2000)

[52] M. Koike, N. Shibata, H. Kato, and Y. Takahashi, “Development of high efficiency GaN-based multiquantum-well light-emitting diodes and their applications,” IEEE J. of Selected Topics in Quantum Electronics, Vol. 8, pp.271-277 (2002)

[53] S. Y. Kim, H. W. Jang, and J. L. Lee, “Effect of an indium-tin-oxide overlayer on transparent Ni/Au ohmic contact,” Appl. Phys. Lett., Vol. 82, pp.61-63 (2003)

[54] C. H. Kuo, S. J. Chang, Y. K. Su, L. W. Wu, J. F. Chen, J. K. Sheu, and J. M. Tsai, “GaN-Based Light Emitting Diodes with Si-Doped In0.23Ga0.77N/GaN,” Jpn. J. Appl. Phys., Vol. 42, pp.2270-2272 (2003)

[55] O. H. Nam, M. D. Bremser, T. S. Zheleva, and R. F. Davis, “Lateral epitaxy of low defect density GaN layers via organometallic vapor phase epitaxy,” Appl. Phys. Lett., Vol. 71, No. 18, pp. 2638-2640 (1997)

[56] C. Huh, J. M. Lee, D. J. Kim, and S. J. Park, “Improvement in light-output efficiency of InGaN/GaN multiple-quantum well light-emitting diodes by current blocking layer,” J. Appl. Phys., Vol. 92, pp. 2248-2250 (2002)

[57] C. M. Lee, C. C. Chuo, Y. C. Liu, I. L. Chen, and J. I. Chyi, “InGaN-GaN MQW LEDs WithCurrent Blocking Layer Formed by Selective Activation,” IEEE Electron. Dev. Lett., Vol. 25, pp. 384-386, (2004)
[58] H. C. Wang, Y. K. Su, C. L. Lin, W. B. Chen, and S. M. Chen “InGaN/GaN Light Emitting Diodes with a Lateral Current Blocking Structure,” Jpn. J. Appl. Phys., Vol. 43, pp. 2006-2008 (2004)

[59] H. Y. Lee, K. H. Pan, C. C. Lin, Y. C. Chang, F. J. Kao, and C. T. Lee, “Current spreading of III-nitride light-emitting diodes using plasma treatment,” J. Vac. Sci. Technol. B, Vol. 25, pp. 1280-1283 (2007)

[60] T. M. Chen, S. J. Wang, K. M. Uang, H. Y. Kuo, C. C. Tsai, W. C. Lee, and H. Kuan, “Current Spreading and Blocking Designs for Improving Light Output Power from the Vertical-Structured GaN-Based Light-Emitting Diodes,” IEEE Photon. Technol. Lett., Vol. 20, pp. 703, (2008)

[61] M. A. Tsai, P. Yu, J. R. Chen, J. K. Huang, C. H. Chiu, H. C. Kuo, T. C. Lu, S. H. Lin, and S. C. Wang “Improving Light Output Power of the GaN-Based Vertical-Injection Light-Emitting Diodes by Mg+ Implanted Current Blocking Layer,” IEEE Photon. Technol. Lett., Vol. 21, No. 11, pp. 688 (2009)

[62] C. F. Tsai, Y. K. Su, and C. L. Lin “Improvement in the Light Output Power of GaN-Based Light-Emitting Diodes by Natural-Cluster Silicon Dioxide Nanoparticles as the Current-Blocking Layer,” IEEE Photon. Technol. Lett., Vol. 21, No. 14, pp. 993 (2009)

[63] H. Amano, M. Kito, K. Hiramatsu and I. Akasaki, “P-type Conduction in Mg-Doped GaN Treated with Low-Energy Electron Beam Irradiation (LEEBI),” Jpn. J. Appl. Phys., Vol. 28, pp. L2112-L2114, (1998)

[64] 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)

[65] S. Ruvimov, Z. Lilliental-Weber, J. Washburn, K. J. Duxstad, E. E. Haller, Z.-F. Fan, S. N. Mohammad, W. Kim, O. Aktas, A. E. Botchkarev, and H. Morkoc, “Microstructure of Ti/Al and Ti/Al/Ni/Au Ohmic contacts for n-GaN,” Appl. Phys. Lett., Vol. 69, pp. 1556-1558 (1996)
[66] 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, pp. 1087-1094, (2003)

[67] R. N. Joshi, V. P. Singh, and J. C. McClure, “Characteristics of indium tin oxide films deposited by r.f. magnetron sputtering,” Thin Solid Films, Vol. 257, pp. 32-35 (1995)

[68] 陳隆建,發光二極體之原理與製程,全華圖書股份有限公司(2008)

[69] Van der Pauw, L. J. , A method of measuring the resistivity and Hall coefficient on lamellae of arbitrary shape. Philips Tech. Rev., Vol. 20, p. 220 (1958)