本論文主要分為兩個研究主題。第一個主題主要是在未圖案化的平面基板上(FSS)和圖案化基板(PSS)上，埋入具有50%高比率空氣洞結構來加以改善藍光、400-nm與380-nm紫外光發光二極體(light-emitting diodes, LED)的相關特性。從SEM與TEM結果觀察，能明顯看到無空氣洞之區域，差排缺陷 (threading dislocations,TDs)會往上延伸。而有空氣洞之區域，差排缺陷會被阻擋住，故此結構能有效降低差排缺陷密度。XRD繞射峰也同樣顯示，埋入空氣洞後，有較低之(002)與(102) 半高寬值，證明了加入空氣洞結構後，能有效改善磊晶材料品質，此結果與SEM與TEM觀察相符。同時，氮化鎵(n=2.38)與空氣洞(n=1)介面之間也會有較高之光反射，進而提升光取出效率。最後，在未圖案化的平面基板上(FSS)和圖案化基板(PSS)上埋入具有50%高比率空氣洞結構後，與傳統圖案化基板(C-PSS)的LED相比，光輸出功率與外部量子效率能有效提升。值得注意地，在可靠度測試方面，當400-nm與380-nm紫外光發光二極體具有空氣洞結構時，與沒有空氣洞結構的發光二極體相比，能明顯改善長時間所造成的光功率衰退與漏電流增加。此技術能有效的商業化並且能供選擇性的取代傳統圖案化基板LED。
在第二個研究主題方面，主要是在討論多重量子井(MQW)中的位障層(Barrier)與發光層(Well)之間加入薄的氮化鋁(銦)鎵埋入層(A(In)GaN interlayer)，並且具有較大能隙的。經由插入漸變的鋁含量(由低至高)的氮化鋁鎵(AlGaN)與氮化鋁(銦)鎵(AlInGaN)埋入層後，與無插入層結構相比，光輸出功率能有效分別提升約70 % 與105%。此重要的效率改善主要是歸功於電子侷限與電洞注入的增加，進而導致在多重量子井中獲得更均勻的分佈。另外，光激發螢光(Photoluminescence, PL)與原子力顯微鏡 (Atomic force microscope, AFM)分析顯示，加入漸變組成的氮化鋁銦鎵(Al(In)GaN)埋入層後，能改善多重量子井的磊晶品質。

This research contains two major topics. Firstly, we analyze the efficiency enhancement of blue light-emitting diodes (LEDs), 400-nm and 380-nm ultraviolet (UV) LEDs by incorporating an air-hole layer within the epitaxial structure. As compared to the conventional patterned sapphire substrate (C-PSS) LEDs and flat sapphire substrate (FSS) LEDs with air-hole, the fabricated patterned sapphire substrate (PSS) LEDs with air-hole exhibit the lowest full width at half maximum (FWHM) of (002) and (102) diffraction peaks, the better light output power, and the highest external quantum efficiency. Remarkable performance improvement in the PSS LED with air-hole is attributed to the better epitaxial quality with threading dislocations terminated by the air-hole structure and the higher scattering at interface between GaN and air-void. In terms of the reliability test after 72 hrs, the decay of the light output power would be outstandingly improved for the 400-nm and 380-nm UV-LEDs. It is well proposed that this methodology provides a promising alternative to C-PSS LEDs.
Secondly, the performance improvement of 380-nm InGaN/AlGaN UV-LEDs are investigated by incorporating an undoped Al(In)GaN thin interlayer between the InGaN well and AlGaN barrier in multi-quantum-well (MQW) active region. By inserting the graded-composition AlGaN and AlInGaN thin interlayers, the light output powers of UV-LEDs are significantly increased by 70% and 105% at 20 mA, respectively, as compared to the LED without the interlayer. Remarkable efficiency enhancement in the UV-LEDs with graded-composition AlGaN and AlInGaN interlayers is mainly attributed to the further improvement of the electron confinement and hole injection with more uniform distribution in the MQW active region. Besides, photoluminescence (PL) and atomic force microscope (AFM) analyses indicate that the MQW quality can be enhanced by incorporating a graded-composition AlInGaN thin interlayer in the MQW active region of UV-LEDs.

Abstract (Chinese)…………………………………..………..I
Abstract (English)………………………………….......…....III Acknowledgements (Chinese)…………………….……...…..V
Contents………………………………………………….......VI
List of Figures…………………………………….…...…..VIII

Chapter 1 Introduction
1.1 Development history of GaN-based light-emitting diodes (LEDs)……………………………………………...………..…1
1.2 Organization of the dissertation…………………………….2

Chapter 2 Epitaxy layers for GaN-based LEDs
2.1 Introduction…………………………………………………3
2.2 Nucleation……………………………………….………….4
2.3 3D and 2D growth by two steps (GaN buffer layer)……......5
2.7 MQW……………………………………………….……....6
2.8 Electron blocking layer……………………………………..7
2.9 P-type layer …………………….……………………..……8

Chapter 3 Efficiency improvement of blue LEDs by using a GaN burried air void photonic crystal with high air filling fraction
3.1 Introduction…………………………………………………9
3.2 Experiment………………………………………………...10
3.3 Results and Discussion……………………………………15
3.3.1 SEM and TEM Analyses of LEDs……………………………..15
3.3.1 Performance Analyses of blue LEDs……………….………….18
3.3.2 Performance Analyses of 400-nm ultraviolet LEDs…………...27
3.3.2 Performance Analyses of 380-nm ultraviolet LEDs………...…35
3.4 Summary………...………………………………………...44

Chapter 4 Performance improvement of 380 nm ultraviolet LEDs by incorporating a thin Al(In)GaN interlayer in MQW
4.1 Introduction………………………………………………..45
4.2 Experiment………………………………………………...47
4.3 Results and Discussion……………………………………50
4.3.1 Performance Analyses by incorporating a thin Al(In)GaN interlayer in MQW…………………………………………………..50
4.3.2 Effect of AlGaN interlayer with differently graded Al- composition methods……………………………………………...…72
4.4 Summary………………………...……………………...…80

Chapter 5 Conclusions and Future Works……...………….82

References………………………………………………….…84

[1] H. Amano, N. Sawaki, I. Akasaki, and Y. 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.
[2] S. Nakamura and M. R. Krames, “History of Gallium–Nitride-based light-emitting diodes for illumination,” Proc. IEEE, vol. 101, pp. 2211–2220, 2013.
[3] S. Nakamura and G. Fasol, ”The blue laser diode,“ Springer-Verlag, 1997.
[4] S. Nakamura, M. Senoh, N. Iwasa, and S. Nagahama, “High-brightness InGaN blue, green and yellow light-emitting diodes with quantum well structures,’’ Jpn. J. Appl. Phys., vol. 34, pp. L797–L799, 1995.
[5] Tetsu Kachi, Kazuyoshi Tomita, Kenji Itoh, and Hiroshi Tadano, ”A new buffer layer for high quality GaN growth by metal organic vapor phase epitaxy,” Appl. Phys. Lett., vol. 72, pp. 704-706, 1998.
[6] S. D. Lester, F. A. Ponce, M. G. Craford, and D. A. Steigerwald, “High dislocation densities in high efficiency GaN-based light-emitting diodes,” Appl. Phys. Lett., vol. 66, pp.1249 -1251, 1995.
[7] T. Böttcher, “Heteroepitaxy of group-iii-nitrides for the application in laser diodes,” University of Bremen, 2002.
[8] J. Chena, S. M. Zhang, B. S. Zhang, J. J. Zhu, X. M. Shen, G. Feng, J. P. Liu, Y. T. Wang, H. Yang, W.C. Zheng “Influences of reactor pressure of GaN buffer layers on morphological evolution of GaN grown by MOCVD,” J. Crystal Growth, vol. 256, pp. 248-253, 2003.
[9] S. Kim, J. Oh, J. Kang, D. Kim, J. Won, J. W. Kim, H. K. Cho, “Two-step growth of high quality GaN using V/III ratio variation in the initial growth stage,” J. Crystal Growth, vol. 262, pp. 7-13, 2004.
[10] T. Yang, K. Uchida, T. Mishima, J. Kasai, J. Gotoh, “Control of Initial nucleation by reducing the V/III ratio during the early stages of GaN growth,” Phys. Stat. Sol. (a), vol. 180, pp. 45-50, 2000.
[11] S. Figge, T. Bottcher, S. Einfeldt, D. Hommel, “In situ and ex situ evaluation of the film coalescence for GaN growth on GaN nucleation layers” J. Crystal Growth, vol. 221, pp. 262-266, 2000.
[12] D.G. Zhao, D.S. Jiang, J.J. Zhu, Z.S. Liu, S.M. Zhang, Hui Yang, J.W. Liang, “The influence of V/III ratio in the initial growth stage on the properties of GaN epilayer deposited on low temperature AlN buffer layer,” J. Crystal Growth, vol. 303, pp. 414-418, 2007.
[13] S. J. Chang, W. C. Lai, Y. K. Su, J. F. Chen, C. H. Liu, and U. H. Liaw, “InGaN–GaN multi quantum-well blue and green light-emitting diodes,” IEEE J. Sel. Topics Quantum Electron, vol. 8, pp. 278-283, 2002.
[14] S. Nakamura, G. Fasol, the blue laser diode, Springer Verlag, Berlin Heidelberg New York, 1997.
[15] S. Keller, B. P. Keller, D. Kapolnek, A. C. Abare, H. Masui, L. A. Coldren, U. K. Mishra, and S. P. Den Baars, “Growth and characterization of bulk InGaN films and quantum wells,” Appl. Phys. Lett., vol. 68, pp. 3147 -3149, 1996.
[16] L. W. Wu, S. J. Chang, T. C. Wen, Y. K. Su, J. F. Chen, W. C. Lai, C. H. Kuo, C. H. Chen, and J. K. Sheu, “Influence of Si-doping on the characteristics of InGaN–GaN multiple quantum-well blue light emitting diodes, IEEE J. Quantum Electron, vol. 38, pp. 446 -450, 2002.
[17] Y. H. Cho, J. J. Song, S. Keller, M. S. Minsky, E. Hu, U. K. Mishra, and S. P. DenBaars, “Influence of Si doping on characteristics of InGaN/GaN multiple quantum wells,” Appl. Phys. Lett., vol. 73, pp. 1128 -1130, 1998.
[18] K. B. Lee, P. J. Parbrook, T. Wang, J. Bai, F. Ranalli, R.J. Airey, G. Hill, “Effect of the AlGaN electron blocking layer thickness on the performance of AlGaN-based ultraviolet light-emitting diodes,” J. Crystal Growth, vol. 311, pp. 2857 -2859, 2009.
[19] S. H. Han, D. Y. Lee, S. J. Lee, C. Y. Cho, M. K. Kwon, S. P. Lee, D. Y. Noh, D. J. Kim, Y. C. Kim, and Seong-Ju Park, “Effect of electron blocking layer on efficiency droop in InGaN/GaN multiple quantum well light-emitting diodes,” Appl. Phys. Lett., vol. 94, pp. 231123-1-231123-3, 1998.
[20] O. Svensk, P. T. Torma , S. Suihkonen, M. Ali, H. Lipsanen, M. Sopanen, M. A. Odnoblyudov, V. E. Bougrov, “Enhanced electro luminescence in 405nm InGaN/GaN LEDs by optimized Electron blocking layer,” J. Crystal Growth, vol. 310, pp. 5154 -5157, 2008.
[21] K. S. Kim, J. H. Kim, S. J. Jung, Y. J. Park, and S. N. Cho, “Stable temperature characteristics of InGaN blue light emitting diodes using AlGaN/GaN/InGaN superlattices as electron blocking layer,” Appl. Phys. Lett., vol. 96, pp. 091104-1- 091104-3, 1998.
[22] Y. K. Kuo, M. C. Tsai, and S. H. Yen, “Numerical simulation of blue InGaN light-emitting diodes with polarization-matched AlGaInN electron-blocking layer and barrier layer,” Optics communications, vol. 282, pp. 4252-4255, 2009.
[23] 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.
[24] W. Gotz, N. M. Johnson, J. Walker, D. P. Bour, and R. A. Street, “Activation of acceptors in Mg-doped GaN grown by metalorganic chemical vapor deposition,” Appl. Phys. Lett., vol. 68, pp. 667 -669, 1996.
[25] C. S. Kim, H. K. Cho, M. K. Yoo, H. S. Cheong, C. H. Hong, and H. K. Cho, “Mg Fluctuation in p-GaN layers and its effects on InGaN/GaN blue light-emitting diodes dependent on p-GaN growth temperature”, Journal of Electronic Materials, vol. 33, pp. 445 -449, 2004.
[26] T. Stephan, K. Kohler, M. Maier, M. Kunzer, P. Schlotter, J. Wagner, “Influence of Mg doping profile on the electroluminescence properties of GaInN multiple quantum well light emitting diodes,” Proceedings of the society of photo-optical instrumentation engineers (SPIE), vol. 5366, pp. 118-126, 2004.
[27] K. Köhler, T. Stephan, A. Perona, J. Wiegert, M. Maier, M. Kunzer, and J. Wagner, “Control of the Mg doping profile in III-N light-emitting diodes and its effect on the electroluminescence efficiency,” J. Appl. Phys., vol. 97, pp. 104914-1-4, 2005.
[28] K. Kim and J. G. Harrison, “Critical Mg doping on the blue-light emission in p-type GaN thin films grown by metal–organic chemical-vapor deposition,” Journal of vacuum science & technology a, vol. 21, pp. 134-139, 2003.
[29] S. Zhou, S. Liu, and H. Ding, “Enhancement in light extraction of LEDs with SiO2 current blocking layer deposited on naturally textured p-GaN surface,” Optics & Laser Technol., vol. 47, pp. 127-130, 2013.
[30] C. M. Tsai, J. K. Sheu, P. T. Wang, W. C. Lai, S. C. Shei, S. J. Chang, C. H. Kuo, C. W. Kuo, and Y. K. Su, “High efficiency and improved ESD characteristics of GaN-based LEDs with naturally textured surface grown by MOCVD,” IEEE Photon. Technol. Lett., vol. 18, pp. 1213-1215, 2006.
[31] C. S. Chang, S. J. Chang, Y. K. Su, C. T. Lee, Y. C. Lin, W. C. Lai, S. C. Shei, J. C. Ke, and H. M. Lo, “Nitride-based LEDs with textured side walls,” IEEE Photon. Technol. Lett., vol. 16, pp. 750-752, 2004.
[32] D. H. Long, I. K. Hwang, and S. W. Ryu, “Design optimization of photonic crystal structure for improved light extraction of GaN LED,” IEEE J. Sel. Topics Quantum Electron, vol. 15, pp. 1257-1263, 2009.
[33] H. W. Huang, C. H. Lin, J. K. Huang, K. Y. Lee, C. C. Yu, and H. C. Kuo, “Improved light output power of GaN-Based light-emitting diodes using double photonic quasi-crystal patterns,” IEEE Electron Device Lett., vol. 30, pp. 1152-1154, 2009.
[34] Y. C. Shin, D. H. Kim, D. J. Chae, J. W. Yang, J. I. Shim, J. M. Park, K. M. Ho, K. Constant, H. Y. Ryu, and T. G. Kim, “Effects of nanometer-scale photonic crystal structures on the light extraction from GaN light-emitting diodes,” IEEE J. Quantum Electron, vol. 46, pp. 1375-1380, 2010.
[35] H. Gao, K. Li, F. M. Kong, X. L. Chen, and Z. M. Zhang, “Improving light extraction efficiency of GaN-based LEDs by AlxGa1−xN confining layer and embedded photonic crystals,” IEEE J. Sel. Topics Quantum Electron, vol. 18, pp. 1650-1660, 2012.
[36] P. A. Shields, M. D. B. Charlton, C. J. Lewins, X. Gao, D. W. E. Allsopp, W. N. Wang, and B. Humphreys, “Effect of coalescence layer thickness on the properties of thin-chip InGaN/GaN light emitting diodes with embedded photonic quasi-crystal structures,” Phys. Status Solidi A, vol. 209, pp. 451-455, 2012.
[37] P. A. Shields, M. D. B. Charlton, T. Lee, M. E. Zoorob, D. W. E. Allsopp, and W. N. Wang, “Enhanced light extraction by photonic quasi-crystals in GaN blue LEDs,” IEEE J. Sel. Topics Quantum Electron., vol. 15, pp. 1269-1274, 2009.
[38] M. Boroditsky, T. F. Krauss, R. Coccioli, R. Vrijen, R. Bhat, and E. Yablonovitch, “Light extraction from optically pumped light-emitting diode by thin-slab photonic crystals,” Appl. Phys. Lett., vol. 75, pp. 1036-1038, 1999.
[39] J. H. Son, J. U. Kim, Y. H. Song, B. J. Kim, C. J. Ryu, and J. L. Lee, “Design rule of nanostructures in light-emitting diodes for complete elimination of total internal reflection,” Adv. Mater., vol. 24, pp. 2259-2262, 2012.
[40] M. Y. Ke, C. Y. Wang, L. Y. Chen, H. H. Chen, H. L. Chiang, Y. W. Cheng, M. Y. Hsieh, C. P. Chen, and J. Huang, “Application of nanosphere lithography to LED surface texturing and to the fabrication of nanorod LED arrays,” IEEE J. Sel. Topics Quantum Electron, vol. 15, pp. 1242-1249, 2009.
[41] O. Lupan, T. Pauporté, and B. Viana, “Low-voltage UV-electro luminescence from ZnO-nanowire array/p-GaN light-emitting diodes,” Adv. Mater., vol. 22, pp. 3298-3302, 2010.
[42] S. H. Han, D. Y. Lee, H. W. Shim, G. C. Kim, Y. S. Kim, S. T. Kim, S. J. Lee, C. Y. Cho, and S. J. Park, “Improvement of efficiency droop in InGaN/GaN multiple quantum well light-emitting diodes with trapezoidal wells,” J. Phys. D: Appl. Phys., vol. 43, pp. 354004-354008, 2010.
[43] Y. Y. Zhang and Y. A. Yin, “Performance enhancement of blue light-emitting diodes with a special designed AlGaN/GaN superlattice electron-blocking layer,” Appl. Phys. Lett., vol. 99, pp. 221103-221105, 2011.
[44] T. Mukai and S. Naksmura, “Ultraviolet InGaN and GaN single-quantum- well-structure light-emitting diodes grown on epitaxially laterally overgrown GaN substrates,” Jpn. J. Appl. Phys., vol. 38, pp. 5735-5739, 1999.
[45] H. Jia, L. Guo, W. Wang, and H. Chen, “Recent progress in GaN-based light-emitting diodes,” Adv. Mater., vol. 21, pp. 4641-4646, 2009.
[46] S. H. Park, Y. T. Moon, D. S. Han, J. S. Park, and M. S. Oh, “Light emission enhancement in blue InGaAlN/InGaN quantum well structures,” Appl. Phys. Lett., vol. 99, pp. 181101-1-3, 2011.
[47] S. F. Chichibu, A. Uedono, T. Onuma, B. A. Haskell, A. Chakraborty, T. Koyama, P. T. Fini, S. Keller, S. P. Denbaars, J. S. Speck, U. K. Mishra, S. Nakamura, S. Yamaguchi, S. Kamiyama, H. Amano, I. Akasaki, J. Han, and T. Sota, “Origin of defect-insensitive emission probability in In-containing (Al,In,Ga)N alloy semiconductors,” Nat. Mater., vol. 5, pp. 810-816, 2006.
[48] W. Guo, M. Zhang, P. Bhattacharya, and J. Heo, “Auger recombination in III-nitride nanowires and its effect on nanowire light-emitting diode characteristics,” Nano Lett., vol. 11, pp. 1434-1438, 2011.
[49] Y. H. Ko, J. H. Kim, L. H. Jin, S. M. Ko, B. J. Kwon, J. Kim, T. Kim, and Y. H. Cho, “Electrically driven quantum dot/wire/well hybrid light-emitting diodes,” Adv. Mater., vol. 23, pp. 5364-5369, 2011.
[50] M. T. Wang, K. Y. Liao, and Y. L. Li, “Growth mechanism and strain variation of GaN material grown on patterned sapphire substrates with various pattern designs,” IEEE Photon. Technol. Lett., vol. 23, pp. 962-964, 2011.
[51] Y. B. Tao, T. J. Yu, Z. Y. Yang, D. Ling, Y. Wang, Z. Z. Chen, Z. J. Yang, and G. Y. Zhang, “Evolution and control of dislocations in GaN grown on cone-patterned sapphire substrate by metal organic vapor phase epitaxy,” J. Cryst. Growth, vol. 315, pp. 183-187, 2011.
[52] T. Jung, L. K. Lee, and P. C. Ku, “Novel epitaxial nanostructures for the improvement,” IEEE J. Sel. Topics Quantum Electron,　vol. 15,　pp. 1073-1079, 2009.
[53] H. W. Huang, J. K. Huang, C. H. Lin, K. Y. Lee, H. W. Hsu, C. C. Yu, and H. C. Kuo, “Efficiency improvement of GaN-based LEDs with a SiO2 nanorod array and a patterned sapphire substrate,” IEEE Electron Device Lett., vol. 31, pp. 582-584, 2010.
[54] C. H. Kuo, Y. A. Chen, J. P. Wu, and L. C. Chang, “Efficiency improvement of near-ultraviolet nitride-based light-emitting-diode prepared on GaN nano-rod arrays by metalorganic chemical vapor deposition,” IEEE J. Quantum Electron, vol. 50, pp. 129-134, 2014.
[55] E. H. Park, J. Jang, S. Gupta, I. Ferguson, and C. H. Kim, “Air-voids embedded high efficiency InGaN-light emitting diode,” Appl. Phys. Lett., vol. 93, pp. 191103-1-191103-3, 2008.
[56] C. H. Chiu, P. M. Tu, C. C. Lin, D. W. Lin, Z. Y. Li, K. L. Chuang, J. R. Chang, T. C. Lu, H. W. Zan, C. Y. Chen, H. C. Kuo, S. C. Wang, and C. Y. Chang, “Highly efficient and bright LEDs overgrown on GaN nanopillar substrates,” IEEE J. Sel. Topics Quantum Electron, vol. 17, pp. 971-978, 2011.
[57] C. H. Chiu, C. C. Lin, H. V. Han, C. Y. Liu, Y. H. Chen, Y. P. Lan, P. Yu, H. C. Kuo, T. C. Lu, S. C. Wang, and C. Y. Chang, “High efficiency GaN-based light-emitting diodes with embedded air voids/SiO2 nanomasks,” Nanotechnol., vol. 23, pp. 045303-045309, 2012.
[58] C. J. Lewins, D. W. E. Allsopp, P. A. Shields, X. Gao, B. Humphreys, and W. N. Wang, “Light extracting properties of buried photonic quasi-crystal slabs in InGaN/GaN LEDs,” J. Display Technol., vol. 9, pp. 333-338 , 2013.
[59] B. Heying, X. H. Wu, L. S. Y. Keller, D. Kapolnek, B. P. Keller, S. P. DenBaars, and J. S. Speck, “Role of threading dislocation structure on the x‐ray diffraction peak widths in epitaxial GaN films,” Appl. Phys. Lett., vol. 68, pp. 4188-4190, 1996.
[60] K. S. Kim, C. S. Oh, K. J. Lee, G. M. Yang, C. H. Hong, K. Y. Lim, and H. J. Lee, “Effects of growth rate of a GaN buffer layer on the properties of GaN on a sapphire substrate,” J. Appl. Phys., vol. 85, pp. 8441-8444, 1999.
[61] M. D. B. Charlton, and S. Lin, “Optimization of pattern geometry and investigations of physical mechanisms contributing to improved light extraction in patterned substrate LEDs,” Proc. SPIE, vol. 7954, pp. 795419, 2011.
[62] M. D. B. Charlton, P. A. Shields, D. W. E. Allsopp, and W. N. Wang, “High- efficiency photonic quasi-crystal light emitting diodes incorporating buried photonic crystal structures,” Proc. SPIE, vol. 7784, pp. 778407, 2010.
[63] T. Muksi, and S. Nakamura,” Ultraviolet InGaN and GaN single quantum well structure light-emitting diodes grown on epitaxially laterally overgrown GaN substrates,” Jpn. J. Appl. Phys., vol. 38, no. 10, pp. 5735-5739, Oct. 1999.
[64] S. Chichibu1, T. Azuhata, T. Sota and S. Nakamura,” Spontaneous emission of localized excitons in InGaN single and multiquantum well structures,” Appl. Phys. Lett., vol. 6968, pp. 643-645, 1996.
[65] Takashi MUKAI, Motokazu YAMADA and Shuji NAKAMURA,” Characteristics of InGaN-Based UV/Blue/Green/Amber/Red light-emitting diodes,” Jpn. J. Appl. Phys., vol. 38, no. 7, pp. 3976–3981, Jul. 1999.
[66] M. F. Huang and T. H. Lu, “Optimization of the active-layer structure for the deep-UV AlGaN light-emitting diodes,” IEEE J. Quantum Electron., vol. 42, no. 8, pp. 820-826, Aug 2006.
[67] T. Wang, Y. H. Liua, Y. Lee, Y. Izumi, J. P. Ao, J. Bai, H. D. Li, and S. Sakai, “Fabrication of high performance of AlGaN/GaN-based UV light-emitting diodes,” J. Crystal Growth, vol. 235, no. 1-4, pp. 177-182, Feb. 2002.
[68] A. Chitnis, J. Sun, V. Mandavilli, R. Pachipulusu, S. Wu, M. Gaevski, V. Adivarahan, J. P. Zhang, and M. Asif Khan, “Self-heating effects at high pump currents in deep ultraviolet light-emitting diodes at 324 nm,” Appl. Phys. Lett., vol. 81, no.18, pp. 3491-3493, Oct. 2002.
[69] Gh. Alahyarizadeh, Z. Hassan, and F. K. Yam, “Improvement of the performance characteristics of deep violet InGaN multi-quantum-well laser diodes using step-graded electron blocking layers and a delta barrier,” J. Appl. Phys., vol. 113, no. 12, pp. 123108-1-123108-8, Mar. 2013.
[70] W. Y. Lin, T. Y. Wang, J. H. Liang, S. L. Ou, and D. S. Wuu, “Analysis of the thickness effect of undoped electron-blocking layer in ultraviolet LEDs,” IEEE Trans. Electron Devices, vol. 61, no. 11, pp. 3790-3795, Nov. 2014.
[71] C. S. Xia, Z. M. S. Li, W. Lu, Z. H. Zhang, and Y. Sheng, “Efficiency enhancement of blue InGaN/GaN light-emitting diodes with an AlGaN-GaN-AlGaN electron blocking layer,” J. Appl. Phys., vol. 111, no. 9, pp. 094503-1-094503-4, May 2012.
[72] J. H. Park, D. Y. Kim, S. Hwang, D. Meyaard, E. F. Schubert, Y. D. Han, J. W. Choi, J. Cho, and J. K. Kim, “Enhanced overall efficiency of GaInN-based light-emitting diodes with reduced efficiency droop by Al-composition-graded AlGaN/GaN superlattice electron blocking layer,” Appl. Phys. Lett., vol. 103, no. 6, pp. 061104-1-061104-4, Aug. 2013.
[73] S. H. Park, Y. T. Moon, D. S. Han, J. S. Park, M. S. Oh, and D. Ahn, “Light emission enhancement in blue InGaAlN/InGaN quantum well structures,” Appl. Phys. Lett., vol. 99, no. 18, pp. 181101-1-181101-3, Oct. 2011.
[74] S. J. Chang, C. H. Kuo, Y. K. Su, L. W. Wu, J. K. Sheu, T. C. Wen, W. C. Lai, J. F. Chen, and J. M. Tsai, “400-nm InGaN–GaN and InGaN–AlGaN multiquantum well light-emitting diodes,” IEEE J. Sel. Topics in Quantum Electron., vol. 8, no. 4, pp. 744-748, Aug. 2002.
[75] Y. K. Fu, Y. H. Lu, R. H. Jiang, B. C. Chen, Y. H. Fang, R. Xua, Y. K. Su, C. F. Lin, and J. F. Chen, “Effect of AlInGaN barrier layers with various TMGa flows on optoelectronic characteristics of near UV light-emitting diodes grown by atmospheric pressure metal organic vapor phase epitaxy,” Solid-State Electron., vol. 62, no. 1, pp. 142-145, Aug. 2011.
[76] G. Liu, J. Zhang, C. K. Tan, and N. Tansu, “Efficiency-droop suppression by using large-bandgap AlGaInN thin barrier layers in InGaN quantum-well light-emitting diodes,” IEEE Photon. J., vol. 5, no. 2, pp. 2201011, Apr. 2013.
[77] J. Z. Liu, M. D. B. Charlton, C. H. Lin, K. Y Lee, C. Krishnan, and M. C. Wu, “Efficiency improvement of blue LEDs using a GaN burried air void photonic crystal with high air filling fraction,” IEEE J. Quantum Electron., vol. 50, no. 5, pp. 314-320, May 2013.
[78] W. J. Wang, C. L. Liao, Y. F. Chang, Y. L. Lee, C. L. Ho, and M. C. Wu, “DLTS analyses of GaN pin diodes grown on conventional and patterned sapphire substrates,” IEEE Electron Device Lett., vol. 34, no. 11, pp. 1376-1378, Nov. 2013.
[79] T. Muksi and S. Nakamura, “Ultraviolet InGaN and GaN single quantum well structure light-emitting diodes grown on epitaxially laterally overgrown GaN substrates,” Jpn. J. Appl. Phys., vol. 38, no. 10, pp. 5735-5739, Oct. 1999.
[80] D. Morita, M. Yamamoto, K. Akaishi, K. Matoba, K. Yasutomo, Y. Kasai, M. Sano, S. Nagahama, and T. Mukai, “Watt-class high-output-power 365 nm ultraviolet light-emitting diodes,” Jpn. J. Appl. Phys., vol. 43, no. 9A, pp. 5945-5950, Sep. 2004.
[81] S. F. Chichibu, A. Uedono, T. Onuma, B. A. Haskell, A. Chakraborty, T. Koyama, P. T. Fini, S. Keller, S. P. Denbaars, J. S. Speck, U. K. Mishra, S. Nakamura, S. Yamaguchi, S. Kamiyama, H. Amano, I. Akasaki, J. Han, and T. Sota, “Origin of defect-insensitive emission probability in In-containing (Al,In,Ga)N alloy semiconductors,” Nat. Mater., vol. 5, pp. 810-816, 2006.
[82] Y. H. Ko, J. H. Kim, L. H. Jin, S. M. Ko, B. J. Kwon, J. Kim, T. Kim, and Y. H. Cho, “Electrically driven quantum dot/wire/well hybrid light-emitting diodes,” Adv. Mater., vol. 23, pp. 5364-5369, 2011.
[83] T. A. Henry, A. Armstrong, A. A. Allerman, and M. H. Crawford, “The influence of Al composition on point defect incorporation in AlGaN,” Appl. Phys. Lett., vol. 100, no. 4, pp. 043509-1-043509-4, Jan. 2012.
[84] D. G. Zhao, Z. S. Liu, J. J. Zhu, S. M. Zhang, D. S. Jiang, H. Yang, J. W. Liang, X. Y. Li, and H. M. Gong, “Effect of Al incorporation on the AlGaN growth by metalorganic chemical vapor deposition,” Appl. Surf. Sci., vol. 253, no. 5, pp. 2452-2455, Dec. 2006.
[85] S. Watanabe, N. Yamada, M. Nagashima, Y. Ueki, C. Sasaki, Y. Yamada, T. Taguchi, K. Tadatomo, H. Okagawa, and H. Kudo, “Internal quantum efficiency of highly-efficient InxGaÀ1xN-based near-ultraviolet light-emitting diodes,” Appl. Phys. Lett., vol. 83, no. 24, pp. 4906-4908, Dec. 2003.
[86] T. Kohno, Y. Sudo, M. Yamauchi, K. Mitsui, H. Kudo, H. Okagawa, and Y. Yamada, “Internal quantum efficiency and nonradiative recombination rate in InGaN-based near-ultraviolet light-emitting diodes,” Jpn. J. Appl. Phys., vol. 51 , pp. 072102-1-072102-7, Jul. 2012.
[87] Y. J. Lee, C. H. Chiu, C. C. Ke, P. C. Lin, T. C. Lu, H. C. Kuo, and S. C. Wang, “Study of the excitation power dependent internal quantum efficiency in InGaN/GaN LEDs grown on patterned sapphire substrate,” IEEE J. Sel. Topics in Quantum Electron., vol. 15, no. 4, pp. 1137-1143, Aug. 2009.
[88] S. Nicolay, E. Feltin, J. F. Carlin, M. Mosca, L. Nevou, M. Tchernycheva, F. H. Julien, M. Ilegems, and N. Grandjean, “Indium surfactant effect on AlN/GaN heterostructures grown by metal-organic vapor phase epitaxy: Applications to intersubband transitions,” Appl. Phys. Lett., vol. 88, no. 15, pp. 151902-1-151902-3, Apr. 2006.
[89] D. M. Graham, P. Dawson, G. R. Chabrol, N. P. Hylton, and D. Zhu, “High photoluminescence quantum efficiency InGaN multiple quantum well structures emitting at 380 nm,” J. Appl. Phys., vol. 101, no. 3, pp. 033516-1 -033516-5, Feb. 2007.
[90] T. Liua, S. Jiaoa, D. Wanga, L. Zhaoa, T. Yangb, and Z. Xiaob, “ Growth and characterization of quaternary AlInGaN multiple quantum wells with different aluminum composition,” Appl. Surface Science, vol. 301, pp. 178-182, May 2013.
[91] S. Nagarajan, M. S. Kumar, Y. J. Choi, S. J. Chung, C. H. Hong, and E. K. Suh, “Al composition dependent structural and electrical properties of InAlGaN/GaN Heterostructures,” J. Phy. D: Appl. Phys., vol. 40, no. 15, pp. 4653-4656, Aug. 2007.
[92] J. Y. Chang and Y. K. Kuo, “Advantages of blue InGaN light-emitting diodes with composition-graded barriers and electron-blocking layer,” Phys. Status Solidi A, vol. 210, no. 6, pp. 1103-1106, Feb. 2013.
[93] H. Y. Chung, K. Y. Woo, S. J. Kim, K. H. Kim, H. D. Kim, and T. G. Kim, “Numerical analysis of InGaN/GaN-based blue light-emitting diode with graded indium composition barriers,” Superlattices and Microstructures, vol. 64, pp.1-6, 2013.
[94] Y. K. Kuo, T. H. Wang, and J. Y. Chang, “Blue InGaN light-emitting diodes with multiple GaN-InGaN barriers,” IEEE J. Quantum Electron., vol. 48, no. 7, pp. 946-951, Jul. 2012.
[95] Y. Y. Zhang and G. R. Yao, “Performance enhancement of blue light-emitting diodes with AlGaN barriers and a special designed electron-blocking layer,” J. Appl. Phys., vol. 110, no. 9, pp. 093104-1 -093104-5, Nov. 2011.
[96] C. H. Wang, C. C. Ke, C. Y. Lee, S. P. Chang, W. T. Chang, J. C. Li, Z. Y. Li, H. C. Yang, H. C. Kuo, T. C. Lu, and S. C. Wang, “Hole injection and efficiency droop improvement in InGaN/GaN light-emitting diodes by band-engineered electron blocking layer,” Appl. Phys. Lett., vol. 97, no.26, pp. 261103–1-261103-3, Dec. 2010.
[97] J. C. Zhang, Y. H. Zhu, T. Egawa, S. Sumiya, M. Miyoshi, and M. Tanaka, “Suppression of the subband parasitic peak by 1 nm i-AlN interlayer in AlGaN deep ultraviolet light-emitting diodes,” Appl. Phys. Lett., vol. 93, no. 13, pp. 131117-1-131117-3, Sep. 2008.