在本論文中，我們製作以原子層沉積的氧化鎵鋅薄膜作為砷化鎵/砷化鋁鎵高頻調變近紅外光發光二極體元件的電流散布層，並探討其對元件特性的影響。其中氧化鎵鋅薄膜呈現約 3.3 x 10-4 Ω-cm 的電阻率及橫向高片電阻7.8 Ω/□；與p型重摻雜砷化鎵之間存在低的特徵接觸電阻值約 1.7 × 10-5 Ω-cm2。為了得知元件中電阻、電容的限制如何影響元件頻寬的特性，我們針對不同發光孔徑的元件進行電流-電壓 (I-V) 及電容-電壓 (C-V) 特性的量測。而在近紅外光發光二極體的元件特性方面，對於有著59、84、109、134、159及184 µm發光孔徑及直徑80 µm焊接墊的元件，在注入電流20 mA的情況下，隨著發光孔徑的增加所呈現的順向偏壓為1.6至1.7 V；串聯電阻值則介於5.3至6.1 歐姆 (Ω)。在- 5 V偏壓下，對於不同發光孔徑面積的元件，總電容 (CT) 分別為11.6、14.4、17.9、21.8及31.8 pF。由於總電容與元件接面的面積成正比，因此由不同發光孔徑面積的元件電容特性，可取得直徑80 µm的焊接墊其焊接墊電容（Cp）值約為8.8 pF。
另外，在注入電流50 mA的情況下，隨著元件發光孔徑的增加顯示其光輸出功率分別為4.6、5.4、5.7、5.8、6.2及6.3 mW。而元件的峰值發光波長約為757 nm，在固定電流25 mA的情況下。 在元件製程設計方面，藉由環型金屬電極的設計及低電阻率的氧化鎵鋅電流散佈層的運用，使得注入到局限區域內的電流密度增加，以致元件頻率響應在50 mA下，隨發光孔徑的增加， 3dB 截止頻寬分別達107.8、90.6、74.6、66.8、48.3與45.4 MHz。
另外，也藉由少數載子生命期的觀點去驗證氧化鎵鋅薄膜在砷化鎵/砷化鋁鎵近紅外光發光二極體電流散布的效果。文中主要也分析了元件發光區域面積，對於少數載子生命期的影響，並進一步求得在定電流下，發光二極體達到3dB頻寬為100 MHz時，所需的元件發光區域面積大小。就我們所製作的近紅外光發光二極體而言，在注入電流分別為 10、20、30、40和50 mA的情況下，達到3dB頻寬為100 MHz所需的元件發光區域面積依序為1.4 x 10-6 、5.1 x 10-6、1.7 x 10-5、3.4 x 10-5及 5.1 x 10-5 cm2。然而，在不同直徑的元件發光區域下，相同的電流密度有相同少數載子生命期，其少數載子生命期與電流密度之間存在著開根號成反比的關係，而與元件發光區域的直徑無關。這也代表著氧化鎵鋅薄膜在近紅外光發光二極體中有良好的電流散布特性，而顯現出元件有較低的接觸電阻和順向導通電壓。

In this dissertation, we investigate the fabrication and characterization of high-frequency modulation of GaAs/AlGaAs near-infrared (NIR) light-emitting diodes (LEDs) by using gallium-doped zinc oxide (GZO) prepared by atomic layer deposition (ALD) as the current-spreading layer. The GZO film reveals a low resistivity of ~ 3.3 x 10-4 Ω-cm, a high sheet resistance of 7.8 Ω/□ in the lateral direction. For the GZO contacts to p+-type GaAs, the minimum specific contact resistance of 1.7 x 10-5 Ω-cm2 is obtained. In order to obtain the device RC-limited bandwidth, we performed the current-voltage (I-V) and capacitance-voltage (C-V) measurements on devices with different aperture diameters. The LEDs with the aperture diameter of 59, 84, 109, 134, 159, and 184 μm, and the same bonding pad diameter of 80 μm have a forward voltage of 1.6-1.7 V and the series resistance of 5.3-6.1 Ω at 20 mA with decreasing the aperture diameter. The total capacitance (CT) in the LEDs with different aperture areas at the reverse bias of 5 V is about 11.6, 14.4, 17.9, 21.8, 26.5, and 31.8 pF, respectively. Since the total capacitance is proportional to the area of junction, the pad capacitance (Cp) with aperture diameter of 80 µm is calculated as about 8.8 pF.
And the LED reveals a light output power of 4.6, 5.4, 5.7, 5.8, 6.2, and 6.3 mW at 50 mA with increasing the aperture diameter, respectively. The measured peak wavelength (λpeak) of the device biased at 25 mA is about 757 nm. By the design of a ring-shaped electrode overlapping with GZO film, the 3-dB frequency (f3dB) for the NIR LED biased at 50 mA decreases with aperture diameter, and achieves a maximum of 107.8, 90.6, 74.6, 66.8, 48.3, and 45.4 MHz owing to the increase of injected current density into the confined region.
However, we evaluate the current spreading of GZO on NIR LEDs from the aspect of minority carrier lifetime. We also analyze the effects of aperture area of the NIR LEDs on minority carrier lifetime and further investigate the required injection current to achieve the 3-dB frequency bandwidth of 100 MHz. As to our fabricated NIR LEDs, the aperture area required to achieve the 3-dB frequency bandwidth of 100 MHz at a driving current of 10, 20, 30, 40, and 50 mA is 1.4 x 10-6, 5.1 x 10-6, 1.7 x 10-5, 3.4 x 10-5, and 5.1 x 10-5 cm2, respectively. At the same injection current density, the LEDs with different aperture areas always exhibit the same minority carrier lifetime, which is inversely proportional to the square root of current density, but not depend on the aperture diameter. It means that the GZO layer plays a good current spreading in the lateral direction from the ohmic contact of NIR LEDs, which shows to the lower contact resistance and lower forward voltage.

[1] R. C. Jao and W. Fang, “Effects of frequency and duty ratio on the growth of potato plantlets in vitro using light emitting diodes,” HortScience, vol. 39, no. 2, pp. 375-379, 2004.
[2] R. J. Bula, D. J. Tennessen, R. C. Morrow and T. W. Tibbitts, “Light Emitting Diodes as A Plant Lighting Source,” in Proc. Int. Lighting in Controlled Environments Workshop, 1994.
[3] N. Kumar and N. R. Lourenco, “LED-based visible light communication system: A brief survey and investigation,” J. Eng. Appl. Sci., vol. 5, No. 4, pp. 296-307, 2010.
[4] http://www.ieee802.org/15/pub/TG7.html
[5] T. P. Lee and A. G. Dentai, “Power and modulation bandwidth of GaAs-AIGaAs high-radiance LED’s for optical communication systems,” IEEE J. Quantum Electron., vol. QE-14, no. 3, pp. 150–159, 1978.
[6] K. D. Choquette, R. P. Schneider, Jr., K. L. Lear, and K. M. Geib, “Low threshold voltage vertical-cavity lasers fabricated by selective oxidation,” Electron. Lett., vol. 30, no. 24, pp. 2043-2044, 1994.
[7] M. Jalonen, M. Toivonen, J. Köngäs, A. Salokatve, and M. Pessa, “Oxide-confined resonant cavity red light-emitting diode grown by solid source molecular beam epitaxy,” Electron. Lett., vol. 33, no. 23 , pp. 1989-1990, 1997.
[8] R. Wirth, C. Karnutsch, S. Kugler, and K. Streubel, “High efficiency resonant-cavity LED’s emitting at 650 nm,” IEEE Photon. Technol. Lett., vol. 13, no. 5, pp. 421-423, 2001.
[9] S. F. Chen, H. L. Syu, C. L. Liao, Y. F. Chang, C. C. Huang, C. L. Ho, and M. C. Wu, “Low specific contact resistance of gallium zinc oxide prepared by atomic layer deposition contact on p+-GaAs for high-speed near-infrared light-emitting diode applications,” IEEE Electron Device Lett., vol. 34, no. 8, pp. 972-974, August 2013.
[10] W. L. Bi, C. L. Ho, and M. C. Wu, “Effects of substrate temperature on the Ga-doped ZnO by atomic layer deposition and the application to blue light-emitting diodes as a current spreading layer,” ECS Solid State Lett., vol. 2, no. 11, pp. Q98-Q100, 2013.
[11] Y. F. Chang, C. L. Liao, C. L. Ho, A. S. Liu, and M. C. Wu, “Effects of passivation layer and rapid thermal annealing on the Ga-doped ZnO films grown by ALD,” ECS J. Solid State Sci. Technol., vol. 2, no. 6, pp. N140-N144, 2013.
[12] J. Y. Kim, Y. J. Choi, H. H. Park, S. Golledge, and D. C. Johnson, “Effective atomic layer deposition procedure for Al-dopant distribution in ZnO thin films,” J. Vac. Sci. Technol. A vol. 28, no. 5, pp. 1111-1114, 2010.
[13] L. H. Xu, G. G. Zheng, J. H. Miao, and F. L. Xian, “Dependence of structural and optical properties of sol-gel derived ZnO thin films on sol concentration,” Appl. Surf. Sci. vol. 258, no. 19, pp. 7760–7765, 2012.
[14] N. Lehraki, M. S. Aida, S. Abed, N. Attaf, A. Attaf, and M. Poulain, “ZnO thin films deposition by spray pyrolysis: Influence of precursor solution properties,” Curr. Appl. Phys. Vol. 12, no. 5, pp. 1283-1287, 2012.
[15] D. K. Lee, S. Kim, M. C. Kim, S. H. Eom, H. T. Oh, and S. H. Choi, “Annealing Effect on the Electrical and the Optical Characteristics of Undoped ZnO Thin Films Grown on Si Substrates by RF Magnetron Sputtering,” J. Korean Phys. Soc. vol. 5, no. 4, pp. 1378-1382, 2007.
[16] J. C. Sun, H. W. Liang, J. Z. Zhao, Q. J. Feng, J. M. Bian, Z. W. Zhao, H. Q. Zhang, Y. M. Luo, L. Z. Hu, and G. T. Du, “Annealing effects on electrical and optical properties of ZnO films deposited on GaAs by metal organic chemical vapor deposition,” Appl. Surf. Sci. vol. 254, no. 22, pp. 7482-7485, 2008.
[17] B. Y. Oh, M. C. Jeong, D. S. Kim, W. Lee, and J. M. Myoung, “Post-annealing of Al-doped ZnO films in hydrogen atmosphere,” J. Cryst. Growth 281(2-4), pp. 475-480, 2005.
[18] M. Ritala, M. Leskelä, J. P. Dekker, C. Mutsaers, P. J. Soininen, and J. Skarp, “Perfectly Conformal TiN and Al2O3 Films Deposited by Atomic Layer Deposition,” Chem. Vapor Deposition 5, no. 1, pp. 7-9, 1999.
[19] M. D. Groner, J. W. Elam, F. H. Fabreguette, and S. M. George, “Electrical characterization of thin Al2O3 films grown by atomic layer deposition on silicon and various metal substrates,” Thin Solid Films vol. 413, pp. 186-197, 2002.
[20] M. D. Groner, F. H. Fabreguette, J. W. Elam, and S. M. George, “Low-Temperature Al2O3 Atomic Layer Deposition,” Chem. Mater., vol., no. 4, pp. 639-645, 2004.
[21] T. Sanada and O. Wada, “Ohmic contacts to p-GaAs with Au/Zn/Au structure,” Jpn. J. Appl. Phys., vol. 19, no. 8, pp. L491-L494, 1980.
[22] K. Y. Yen, C. H. Chiu, C. W. Li, C. H. Chou, P. S. Lin, T. P. Chen, T. Y. Lin, and J. R. Gong, “Performance of InGaN/GaN MQW LEDs using Ga-doped ZnO TCLs prepared by ALD,” IEEE Photon. Technol. Lett., vol. 24, no. 23, pp. 2105-2108, 2012.
[23] E. Havard, T. Camps, V. Bardinal, L. Salvagnac, C. Armand, C. Fontaine and S. Pinaud, “Effect of thermal annealing on the electrical properties of indium tin oxide (ITO) contact on Be-doped GaAs for optoelectronic applications,” Semicond. Sci. Technol., vol. 23, pp. 035001-1-035001-4, 2008.
[24] H. C. Casey, Jr. and F. Stern, “Concentration‐dependent absorption and spontaneous emission of heavily doped GaAs,” J. Appl. Phys., vol.47, pp.631-643, 1976.
[25] T. P. Lee and A. G. Dentai, “Power and modulation bandwidth of GaAs-AlGaAs high-radiance LED’s for optical communication systems,” IEEE J. Quantum Electron., vol. 14, pp. 150-159, 1978.
[26] L. B. Chang, D. H. Yeh, L. Z. Hsieh, and S. H. Zeng, “Enhanced modulation rate in platinum-diffused resonant-cavity light-emitting diodes,”J. Appl. Phys., vol. 98, pp. 093504, Nov. 2005.
[27] C. L. Tsai, C. W. Ho, C. Y. Huang, F. M. Lee, M. C. Wu, H. L. Wang, S. C. Ko, W. J. Ho, J. Huang, and J. R. Deng, “Fabrication and characterization of 650 nm resonant-cavity light-emitting diodes,” J. Vac. Sci. Technol., B 22, no. 5, pp. 2518-2521, 2004.
[28] R. Wirth, B. Mayer, S. Kugler and K. Streubel,“Fast LEDs for polymer optical fiber communication at 650 nm,”In Proc. of SPIE, vol. 6013, pp. 60130F1-8, 2005.
[29] C. L. Liao, Y. F. Chang, C. L. Ho, and M. C. Wu, “High-speed GaN-based blue light-emitting diodes with a gallium-doped ZnO current spreading layer,” IEEE Electron Device Lett., vol. 34, no. 5, pp. 611-613, May 2013.
[30] S. J. Chang, C. S. Chang, Y. K. Su, P. T. Chen, Y. R. Wu, K. H. Huang and T. P. Chen, “Chirped GaAs-AlAs distributed Bragg reflectors for high brightness yellow-green light-emitting diodes,” IEEE Photon. Tech. Lett. Vol. 9, pp. 182, 1997.
[31] Thompson G. H. B. Physics of Semiconductor Laser Devices (John Wiley and Sons, New York, 1980)
[32] Rensselaer Polytechnic Institute, Troy, New York, “LIGHT-EMITTING DIODES,’’ Second Edition, E. Fred Schubert.
[33] Goldberg Yu. A. Handbook Series on Semiconductor Parameters, vol.2, M. Levinshtein, S. Rumyantsev and M. Shur, ed., World Scientific, London, 1999, pp. 1-36.
[34]http://www.ee.buffalo.edu/faculty/cartwright/java_applets/quantum/numerov/index.html
[35] T.Sanada and O. Wada, “Ohmic Contacts to p-GaAs with Au/Zn/Au Structure,” Jpn. J. Appl. Phys., vol. 19, no.8, pp. L491-L494, 1980.
[36] K. R. Linga, G. H. Olsen, V. S. Ban, A. M. Joshi, “Dark Current Analysis and Characterization of InxGa1-xAs/InAsyP1-y Graded Photodiodes with x > 0.53 for Response to Longer Wavelengths ( > 1.7 µm),” J. Lightwave Technology., vol. 10, no. 8, 1992.
[37] K. Hild, T. E. Sale, S. J. Sweeney, M. Hirotani, Y. Mizuno, and T. Kato, “Modulation speed and leakage current in 650 nm resonant-cavity light emitting diodes,” IEE Proc.-Optoelectron., vol. 151, no.2, pp. 94-97, Apr. 2004.
[38] G. Blume, T. J. C. Hosea, S. J. Sweeney, P. de Mierry, and D. Lancefield, “AlGaInN resonant-cavity LED devices studied by electromodulated reflectance and carrier lifetime techniques,” IEE Proc.-Optoelectron., vol. 152, no.2, pp. 118-124, May 2005.