在LED的結構中，在沒有GaP window layer情況下，Vf偏高，亮度也較差；相對地成長了GaP window layer的LED，Vf會變低，亮度也明顯增加許多，這是因為window layer可以改善current spreading效果，電流不會侷限在電極下面，同時GaP在材料特性上可以允許有較高的電洞注入和快速的移動性(mobility)，因此Vf表現上可以較低。假如要再提昇亮度，可以應用破壞全反射觀念將GaP加厚改變光的出光位置；然而這對使用MOCVD來說，需要很長的磊晶時間，如何有效提昇亮度，同時又縮短製程時間是本研究要探討的方向。
在本研究中利用粗化LED表面的觀念來研究粗糙表面如何影響 光電特性，改變GaP磊晶條件創造表面不同粗糙狀態，探討粗糙度與亮度關係。實驗結果指出，控制GaP的磊晶條件確實會影響LED表面粗糙狀態，對亮度的影響是一種破壞全反射的觀念，但是當粗糙狀態超過一個程度後，影響的效果就會不明顯，因為光再度受全反射影響反射回LED本體被材料吸收；另外也使用溼蝕刻製程了解在特定的蝕刻液下，對表面粗化情形，結果同樣具有提升亮度的幫助，所以有效掌控粗化製程條件，就能提昇亮度表現，但是相對磊晶製程來說，無疑是多了一道製程時間。

In LED structure, if there is no GaP window layer, the Vf is high and the luminous intensity is lower. So we usually epis the GaP window layer under the P-type as the current spreading layer. The LED has the low Vf and high luminous intensity in the GaP window layer because window layer can improve the current spreading effect which the current can’t blocked under the electrode. The GaP material has the higher doping and high speed mobility in p-type. We can improve the luminous intensity by making thicker GaP window layer thickness which changes the light extracts position by the total internal reflection. But this technology needs more epitaxy time in MOCVD system. How to improve luminous intensity efficiently and shorten the process hours is my aspect in study.
I use the roughness technology to study how the rough surface affects the LED luminous intensity. The technology uses the GaP epitaxy growth condition to make the surface roughness and study the relationship between the rough surface and the luminous intensity. In the experiment, we can change the LED surface roughness by controlling the GaP growth condition. And how does the roughness affect the luminous intensity uses the destroying the total internal reflection. But the roughness impression can’t affect the luminous intensity until the out angle is over the critical angle which causes the total internal reflection. When the light reflects to the body, it will be absorbed by the material. I also used the wet etching solution to study how it made the rough surface and the luminous intensity. So we can improve the LED brightness performance just by controlling the roughness process condition. So the wet etching also improved the LED luminous intensity, however it need more the process than the epitaxy process.

[1] Lin, Jyh-Feng (National Tsing Hua University), Wu, Meng-Chyi, Jou, Ming-Jiunn, Chang, Chuan-Ming, Lee, Biing-Jye(1994,Spet). Growth of a GaP window layer on AlGaInP light-emitting diodes using misoriented substrates. Journal of Crystal Growth, 142, 15-20
[2] Huang, K.H., Yu, J.G., Kuo, C.P., Fletcher, R.M., Osentowski, T.D., Stinson, L.J., Craford, M.G., Liao, A.S.H(1992,Aug). Twofold efficiency improvement in high performance AlGaInP light-emitting diodes in the 555-620 nm spectral region using a thick GaP window layer. Applied Physics Letters, 61, p 1045
[3] Fujii, T. (Materials Department, University of California), Gao, Y., Sharma, R., Hu, E.L., DenBaars, S.P., Nakamura, S(2004,Feb). Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening. Applied Physics Letters, 84, 855-857
[4] Fletcher, R.M. (Hewlett-Packard Optoelectronics Div), Kuo, C.P., Osentowski, T.D., Huang, K.H., Craford, M.G., Robbins, V.M.(1991,Dec). Growth and properties of high performance AlGaInP emitters using a lattice mismatched GaP window layer. Journal of Electronic Materials, 20, 1125-1130
[5] Schnitzer, I. (University of California), Yablonovitch, E., Caneau, C., Gmitter, T.J., Scherer, A.(1993,Oct). 30% External quantum efficiency from surface textured, thin-film light-emitting diodes. Applied Physics Letters, 63, 2174-2176
[6] Qingke, Zeng (Guangxi Normal University), Xianfu, Zeng, Changjun, Liao, Songhao, Liu, Manufacture of AlGaInP visible light-emitting diodes by MOCVD & VPE. Solid-State Electronics: An International Journal, 42, 993-995
[7] Hsieh, Li-Zen (Department of Electrical Engineering, Chung-Cheng Institute of Technology, National Defense University), Chang, Li-Yuan(2003,Sept). The comparisons between GaP window layers of double-heterojunction light-emitting diodes using various dopants and source melts regrown by indium-addition liquid phase epitaxy. Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers, 42, 5709-5713
[8] Lee, Chong-Yi (Natl Tsing Hua University), Wu, Meng-Chyi, Lin Wei (1999,April). Influence of window layers on the performance of 650 nm AlGaInP/GaInP multi-quantum-well light-emitting diodes. Journal of Crystal Growth, 200, 382-390
[9] Chang, S.J. (National Cheng Kung University), Chang, C.S., Su, Y.K., Chang, P.T., Wu, Y.R., Huang, K.H., Chen, T.P.(1997,Dec). AlGaInP multiquantum well light-emitting diodes. IEE Proceedings: Optoelectronics, 144, 405-409
[10] Hsieh, L.Z. (Department of Electrical Engineering, Chung-Cheng Institute of Technology, National Defense University), Chang, L.Y.(2002). The characteristics of GaP window layer grown by indium-added liquid phase epitaxy. Crystal Research and Technology, 37, 921-927
[11] C.C.Sun,and C.Y.Lin(2004). Light extraction of an LED with surface roughening and sharpening. Proc.SPIE 5187, 100-106
[12] Wierer, J.J. (LumiLeds Lighting), Bhat, J.C., Chen, C.-H., Christenson, G., Cook, L.W., Craford, M.G., Gardner, N.F., Gotz, W., Kern, R.S., Khare, R., Kim, A., Krames, M.R., Ludowise, M.J., Mann, R., Martin, P.S., Misra, M., O'Shea, J., Shen, Y.C., Steranka, F.M., Stockman, S.A., Subramanya, S., Rudaz, S.L., Steigerwald, D.A., Yu, J.(2001). High-power AlInGaN light-emitting diodes. Proceedings of SPIE - The International Society for Optical Engineering. 4278, 127-132
[13] Huang, Man-Fang (Visual Photonics Epitaxy Co, Ltd), Liu, Pin-Hui, Liu, J. S., Kuo, Yen-Kuang, Huang, Ya-Lien, Chang, Yuni, Huang, Hsu-Ching, Horng, Kuo-Kai, Chang, Jih-Yuan(2000). Experimental and numerical study on the optical properties of yellow-green AlGaInP light emitting diodes. Proceedings of SPIE - The International Society for Optical Engineering, 4078, 595-602
[14] Gessmann, Th. (Department of Electrical Engineering, Rensselaer Polytechnic Institute), Schubert, E.F.(2004,Mar). High-efficiency AlGaInP light-emitting diodes for solid-state lighting applications. Journal of Applied Physics. 95, 2203-2216
[15] Streubel, Klaus (Osram Opto Semiconductor, OSSE1), Linder, Norbert, Wirth, Ralph, Jaeger, Arndt(2002,Mar). High brightness AlGaInP light-emitting diodes. IEEE Journal on Selected Topics in Quantum Electronics, 8, 321-332
[16] Vanderwater, D.A. (Hewlett-Packard Co), Tan, I.-H., Hofler, G.E., Defevere, D.C., Kish, F.A.(1997,Nov). High-brightness AlGaInP light emitting diodes. Proceedings of the IEEE, 85, 1752-1764
[17] Chang, S.J. (National Cheng Kung University), Chang, C.S., Su, Y.K., Chang, P.T., Wu, Y.R., Huang, K.H., Chen, T.P.(1997,Dec). AlGaInP multiquantum well light-emitting diodes. IEE Proceedings: Optoelectronics, 144, 405-409
[18] Su, Yan-Kuin (Department of Electrical Engineering, Institute of Microelectronics, National Cheng Kung University), Wang, Hsin-Chuan, Lin, Chun-Liang, Chen, Wen-Bin, Chen, Shi-Ming(2003,Jul). AlGaInP light emitting diode with a modulation-doped superlattice. Japanese Journal of Applied Physics, 42, 751-753
[19] Beccard, R. (AIXTRON AG), Protzmann, H., Schmitz, D., Strauch, G., Heuken, M., Juergensen, H.(1998). Growth of AlInGaP in multiwafer planetary reactors. Conference Proceedings - International Conference on Indium Phosphide and Related Materials. 575-578
[20] Schineller, B. (RWTH-Aachen), Junas, Y., Heuken, M., Heime, K.(1998,Feb). Investigation of process technologies for the fabrication of AlGaInP mesa ultra high brightness light emitting diode. Materials Science & Engineering B: Solid-State Materials for Advanced Technology, 51, 34-38
[21] Sun, Ching-Cherng (Institute of Optical Sciences, National Central University), Lin, Chao-Ying(2004). Optical modeling and light extraction of an LED with surface roughening and sharpening. Proceedings of SPIE - The International Society for Optical Engineering, 5187, 100-106
[22] Stringfellow, G. B.(1976,Jul-Aug). Effect of surface treatment treatment on surface recombination velocity and diode leakage current in GaP. Journal of Vacuum Science and Technology, 13, 908-913
[23] Hsieh, L.Z. (Department of Electrical Engineering, Chung-Cheng Institute of Technology, National Defense University), Chang, L.Y.(2002). The characteristics of GaP window layer grown by indium-added liquid phase epitaxy. Crystal Research and Technology, 37, 921-927
[24] Lee, Y.J. (Department of Photonics, Institute of Electro-Optical Engineering, National Chiao Tung University), Kuo, H.C., Wang, S.C., Hsu, T.C., Hsieh, M.H., Jou, M.J., Lee, B.J.(2005,Nov). Increasing the extraction efficiency of AlGaInP LEDs via n-side surface roughening. IEEE Photonics Technology Letters, 17, 2289-2291
[25] Lee, Y.J. (Department of Photonic, Institute of Electro-Optical Engineering, National Chiao Tung University), Lu, T.C.; Kuo, H.C., Wang, S.C., Hsu, T.C., Hsieh, M.H., Jou, M.J., Lee, B.J.(2007,Mar). Nano-roughening n-side surface of AlGaInP-based LEDs for increasing extraction efficiency. Materials Science and Engineering B: Solid-State Materials for Advanced Technology, 138, 157-160
[26] Huang, Hung-Wen (Department of Photonics, Institute of Electro-Optical Engineering, National Chiao Tung University), Chu, Jung-Tang, Kao, Chih-Chiang, Hsueh, Tao-Hung, Lu, Tien-Chang, Kuo, Hao-Chung, Wang, Shing-Chung, Yu, Chang-Chin, Kuo, Shou-Yi(2006,Apr). Enhanced light output in InGaN/GaN light emitting diodes with excimer laser etching surfaces. Japanese Journal of Applied Physics, 45, 3442-3445
[27] Hung-Wen Huang, C.C. Kao, J.T. Chu, H.C. Kuo, S.C. Wang, C.C. Yu(2005,May). Improvement of InGaN-GaN light-emitting diode performance with a nano-roughened p-GaN surface. Photonics Technology Letters, IEEE, 17, 983 - 985