臺灣博碩士論文加值系統

在這篇論文中，我們研究有關c軸平面氮化銦薄膜與a軸平面氮化銦薄膜之光激發產生兆赫波輻射研究。我們的團隊曾報導過源自於奈米柱狀結構的兆赫波輻射強度增強現象，相較於c軸平面氮化銦薄膜所展生者在兆赫波輻射電場上大上十倍，並且我們認為這兩種結構的氮化銦薄膜都是以photo-Dember effect作為輻射兆赫波的主要機制。對於沿著a軸 成長的平面而言，極化導致的電場平行於表面介面，我們並且發現其兆赫波放射能量上遠遠比c軸平面氮化銦薄膜大上兩個級數，且與目前所知最好的兆赫波放射源：砷化銦擁有相同級數的輻射強度。我們認為a軸平面氮化銦薄膜主要的兆赫波輻射機制是來自於受激發載子在極化感應電場下有著較為有效率輻射出半導體介面的幾何耦合輻射效應。

在高能量雷射的激發之下，放射出的兆赫波顯示出與方位角有關的分量疊加於與方位角無關的分量上。與激發光線的線性偏振和方位角有關的兆赫波輻射特性可能是來自於兆赫波的非線性輻射，例如光整流效應，此與a軸平面氮化銦薄膜的電納系數有著密切關係。

In this thesis, we report the terahertz emission measurement from c-plane and a-plane indium nitride (InN) films. Our group already has reported the enhancement of terahertz (THz) radiation (greater than ten times in intensity) from InN nanorod arrays compared to the InN films grown along the c-axis and the dominant emission mechanism was proposed to be the photo-Dember effect. For the layers grown along a-( ), polarization-induced electric field is parallel to the layer interface and THz emission from it is found to be at least two orders of magnitude stronger than that from c-plane InN film, which is the same order of InAs, the best semiconductor THz emitter so far. We propose that the primary radiation mechanism of the a-plane InN film is due to the acceleration of photoexcited carriers under the polarization-induced in-plane electric field perpendicular to the a-axis, which effectively enhances the geometrical coupling of the radiation out of semiconductor.
At high photoexcitation, emitted THz wave shows the obvious azimuthal angle dependence superimposed with a strong angle-independent component. Pump polarization and azimuthal angle dependence of emitted THz wave may be due to the nonlinear THz emission mechanism, such as optical rectification, which is depending on the characteristic susceptibility tensor of a-plane InN.

Abstract(C)...............................................i
Abstract(E) .............................................ii
Acknowledgement.........................................iii
Contents.................................................iv
List of Figures..........................................vi
List of Tables............................................x
Chapter 1 Introduction ...................................1
1-1 Terahertz Radiation...................................1
1-2 III-Nitride Compound Semiconductors : InN.............5
1-3 Organization of Thesis................................7
Chapter 2 Experimental Theories ..........................8
2-1 Terahertz Generation..................................8
2-1-1 Surge-Current Model.................................8
2-1-2 Surface Depletion Field............................10
2-1-3 Photo-Dember Effect................................12
2-1-4 Optical Rectification..............................16
2-1-5 THz Enhancement by External Magnetic Field ........19
2-2 Terahertz Detection : Electro-Optical Crystal and Free Space Electro-Optic Sampling (FS-EOS)................... 21
Chapter 3 Experimental Setups ...........................25
3-1 Introduction of Femtosecond Laser System.............25
3-2 Electro-Optic THz System.............................27
Chapter 4 Sample Properties..............................31
4-1 InN Film (c-plane InN)...............................33
4-2 Nonpolar InN Film (a-plane InN)......................34
Chapter 5 Experimental Results and Discussion............37
5-1 Terahertz Emission from InN Surface .................37
5-2 Azimuthal Angle dependence of InN....................45
5-3 Pump Polarization Dependence of Semiconductors.......51
Chapter 6 Conclusion and Future Work.....................55
6-1 Conclusion ..........................................55
6-2 Future Work..........................................56

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