現代社會依賴無線網路傳輸資訊的需求日益上升，然而現今無線通訊頻段已十分擁擠，為追求更快的無線傳輸率並解決無線傳輸通道擁塞的問題，高頻段之無線通訊系統有充分被研究之價值。太赫茲段介於傳統微波通訊波段以及紅外線波段之間，由於此頻段尚未列入通訊系統規範，且因高頻特性使其可乘載之訊號比傳統無線微波通訊更多，與鄰近之更高頻的紅外線波段相比，太赫茲具有更長遠之無線傳輸距離，然而不同於已成熟發展之微波通訊以及光纖通訊，目前仍缺乏有實用價值的太赫茲輻射源。
本研究著重在開發鍺基太赫茲輻射源，光電導太赫茲輻射源為產生兆赫輻射的元件種類之一，其能實現可攜式、高功率太赫茲通訊元件，傳統光電導太赫茲輻射源受限於低量子轉換效率，而光柵結構可大幅提高轉換效率，另外鍺基半導體能與1550 nm光通訊波段結合，相較於銦砷化鎵光電導兆赫輻射源，鍺基半導體在製程上能與現有電子元件整合，並且在輻射頻譜上能夠涵蓋更高頻之波段範圍。由於鍺為間接能隙半導體，載子生命週期約為數百微秒，遠大於直接能隙半導體，因此難以用脈衝重複率高的飛秒雷射或是連續波雷射激發，我們利用氧氣與氬氣對鍺半導體表面進行物理性轟擊，破壞表面晶格結構，達到降低載子生命週期的效果，並實現鍺基光電導太赫茲輻射源。

Data transmission relies on wireless data transfer is in an upward trend in modern society. However, it is very crowded in the channels of wireless communication bands of nowadays. In order to pursue higher data transfer rate and find out the solution for wireless communication channel congestion, it is worth doing research on wireless communication in high frequency band. Terahertz (THz) band is between microwave and infrared; since this frequency band has not allocated, and the high carrier frequency allows it carriers more information than microwave communication. Moreover, THz wave is able to transmit in a longer distance compare to infrared. In comparison with well-developed microwave communication and fiber-optic communication, a lack of practical THz source limits the development of THz communication.
This thesis focuses on the development of Ge photoconductive THz source. Photoconductive THz source is a kind of devices for THz wave generation. It is able to realize portable and high power THz source. Conventional photoconductive THz source is limited by the low conversion efficiency, and the grating structure is able to enhance the conversion efficiency. By use of Ge as the photoconductor allows the device to combine with 1550 nm optical communication system. Compared to InGaAs photoconductive THz source, the fabrication process of Ge photoconductive THz source is able to combine with modern complementary metal oxide semiconductor (CMOS) fabrication process. Moreover, it covers the wider bandwidth and it can reach higher frequency of THz radiation. Nevertheless, Ge is a kind of indirect band gap semiconductor, the carrier lifetime is around several hundred microsecond, which is much greater than the direct band gap semiconductor, and it is hard to generate THz radiation by using high repetition rate femtosecond laser and continuous wave (CW) laser as the pumping source. O2 and Ar plasma are used to bombard the surface of Ge, destroying the crystal quality of Ge to shorten the carrier lifetime. The device after carrier lifetime shortened treatment is discussed analytically in this thesis.

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