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研究生:許立佐
研究生(外文):Li-Tso Hsu
論文名稱:利用時間解析量測一微米厚氧化鋅薄膜之超快載子動力學研究
論文名稱(外文):Ultrafast Dynamics of 1um ZnO Epitaxial Films by Time-Resolved Measureme
指導教授:林家弘林家弘引用關係
口試委員:洪魏寬吳小華謝文峰
口試日期:2009-07-06
學位類別:碩士
校院名稱:國立臺北科技大學
系所名稱:光電工程系研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2009
畢業學年度:97
語文別:英文
論文頁數:34
中文關鍵詞:載子的熱化時間能隙填滿能隙重整自發性輻射射時間自由激子熱化時間聲子協助的穿隧效應深層缺陷吸收
外文關鍵詞:hot carrier cooling timeband-fillingband-gap renormalizationpontaneous emissionexciton thermalizationphonon-assisted-tunnelingdefect absorption
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在本篇論文中,我們以飛秒短脈衝雷射為激發光源,並利用時間解析的量測技術來研究於室溫下在氧化鋅薄膜材料中的超快載子動力行為,當光子的激發能量高於氧化鋅的能隙時(above band-gap),我們由所得到的時間解析的反射率,得到載子在受激發後會產生能隙填滿(band-filling)與能隙重整的效應,而且這兩個效應會有競爭的現象發生;利用三分量分解法,得到載子的熱化(聲子-光子的散射)時間約1.2皮秒,能隙重整恢復(band-gap renormalization recovery) 時間約4.8皮秒,最後是一個非常長的自發性輻射射時間大約100皮秒左右;當激發光子的能量落在激子的能量時(near exciton),我們則觀察到1皮秒的自由激子熱化時間,以及約50皮秒的能隙重整恢復時間;當激發光子的能量在淺層能隙尾部時 (shallow band tail),利用所得到的穿透率的時間解析圖形,觀察到載子在受激發後會發生藉由聲子協助的穿隧效應,以及深層缺陷的吸收會使得穿透率將低;當光子的激發能量在深的能隙尾部區域 (deep band tail),由於缺陷所造成的吸收飽和現象會使得穿透率變為正值.
In thesis, we used femtosecond-laser as the light source to investigated the ultrafast carrier dynamics of ZnO thin films at room temperature by using time-resolved measurement technology. As the photo-excited energy is above band-gap of ZnO, the effect of band-filling and bandgap renormalization will occur simultaneously and compete each other that can be seen in time resolved photo-reflectance change while the carrier is excited from the valence band to the conduction bnad. By decomposition the trace with three components, we obtain the hot carrier cooling about 1.2 ps followed by BGR recovery about 4.8 ps, and a relative long time scale about 100 ps which is spontaneous emission. As the photo-excited energy is located near exciton states, we observed relative short decay time about 1 ps due to exciton thermalization, and a slow recovery time of 50 ps due to free exciton spontaneous emission (SPE). As the photo-excited energy is located in shallow band-tail states, it showed the behavior of phonon-assisted-tunneling and defect absorption. In deep band-tail states, the positive transmission change can be seen by the effect of BF due to absorption saturation of defect level.
Chinese abstract........................I
English abstract........................II
Contents........................III
List of figures........................IV
Chapter 1 Introduction........................1
1.1 Optical properties of zinc oxide..........1
1.1.1 Why Choose ZnO material........................1
1.2 Time-resolved spectroscopy in semiconductors.......2
1.2.1 Why studying ultrafast carrier dynamics.......2
1.2.2 Temporal evolution in semiconductors.......2
1.3 Time Resolved measurement of ultrafast carrier dynamics.......4
1.3.1 Review of TRPL in ZnO thin films.......5
1.3.2 Review of pump-probe in ZnO thin films.......7
1.4 Motivation.......8
References.......10
Chapter 2 Theoretical background.......12
2.1 Free carrier induced effects.......12
2.1.1 Band-filling effect.......12
2.1.2 Band-gap renormalization.......13
2.2 How to measure ultrafast dynamics.......14
References.......16
Chapter 3 Experimental setup.......17
Chapter 4 Experimental result and discussion.......19
4.1 Absorption and photoluminescence.......19
4.2 Above band-gap dynamics.......20
4.3 Near-exciton resonance dynamics.......26
4.4 Shallow band-tail dynamics.......29
4.5 Deep band- tail dynamics.......31
References.......33
Chapter 5 Conclusion.......34
Chapter 1

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[1.9]K. T. Tsen, Ultrafast Physical Processes in Semiconductors, Academic Press, 2001.
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[1.11]T. T. Yao et al., “Dynamics of Photoexcited High Density Carriers in ZnO Epitaxial Thin Films,” Physica Status Solidi (b), vol. 229, no. 2, pp. 877-880.
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Chapter 2

[2.1]A. Yariv, Optical Electronics. 3rd ed. New York: Holt. Rinehart and Winston, 1985, pp. 474-478.
[2.2]P. A. Wolff, “Theory of the band structure of very degenerate semiconductors,” Phys. Rev.126. 1962, pp. 405-412.


Chapter 4

[4.1]A. Yamamoto, T. Kido, T. Goto, Y. Chan, T. Yao, and A. Kasuya, “Dynamics of photoexcited carriers in ZnO epitaxial thin films,” Applied Physics Letters vol. 75, no. 4, 1999 pp. 469-471.
[4.2]J. C. Johnson, K. P. Knutsen, H. Yan, M. Law, Y. Zhang, P. Yang, and R. J. Saykally, “Ultrafast Carrier Dynamics in Single ZnO Nanowire and Nanoribbon Lasers,” Nano Letters, vol. 4, no. 2, 2004, pp. 197.
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[4.6]J. Takeda, N. Arai, Y. Toshine, H. Ko and T. Yao, “Ultrafast Dynamics of Exciton–Exciton and Exciton–Longitudinal Optical-Phonon Scattering Processes in ZnO Epitaxial Thin Films,” Japanese Journal of Applied. Physics, vol. 45, no. 9A, 2006, pp. 6961-6963.
[4.7]C. Sun, J. C. Liang, X. Y. Yu, S. Keller, U. K. Mishra, and S. P. DenBaars, “Studies of carrier dynamics in unintentionally doped gallium nitride bandtail states,” vol. 78, no. 18, 2001, pp. 2724-2726.
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