近二十年來，太赫茲頻段的電磁波已經展示其他波段無法達成的優異特性，例如
非破壞性透視成像、化學成分分析以及6G 高速無線通訊。而光電導天線因為其
寬頻、室溫操作以及體積輕巧的優勢，成為最常見寬頻的太赫茲發射器之一。為
了實現寬頻操作，光電導天線PCA 的候選材料通常需要具有超快的載子生命週
期，以將飛秒脈衝雷射光源轉換為亞皮秒級的脈衝電流饋入天線，並輻射出太赫
茲波段的電磁波。為達成這個目標，傳統的光電導材料主要是在超高真空環境下
通過分子束磊晶的低溫生長（LT）或過渡金屬摻雜的III-V 族材料，需要精確控
制磊晶條件並透過高溫退火工藝才能獲得高質量的結構。因此，複雜的製造工藝
和耗時的性質導致極高製造成本，阻礙了太赫茲光電導天線通過成熟的互補式金
屬氧化物半導體工藝大規模生產和完全商業化。雖然有一些團隊提出鍺基太赫茲
光電導天線，但是由於鍺為間接能隙半導體，並且由於其能隙邊界靠近最常用的
1550 nm 雷射光，導致吸收係數大幅下降，進而使光子轉換電子效率降低，這使
得鍺這個光電導材料無法有效率地與體積輕巧並高性價比的1550nm 光通訊波段
飛秒雷射整合。在這篇論文中，我提出第一個基於鍺錫合金的電漿子太赫茲光電
導天線雛形，透過低成本熱蒸鍍的方式沉積光電半導體，並利用光柵結構產生電
漿子效應，大幅提高光轉換至太赫茲的效率，相較於傳統銦砷化鎵光電導太赫茲
天線，鍺錫可以在製程上能與現有的矽製程高度整合，同時也比傳統的鍺基元件
有更好的吸收，使得其非常適合作為量產型的太赫茲元件。

In the past two decades, electromagnetic waves in the terahertz (THz) band have demonstrated excellent characteristics that other bands cannot achieve, such as nondestructive imaging, chemical composition analysis, and 6G high-speed wireless communication. The photoconductive antenna has become one of the most common
broadband THz transmitters because of its advantages in broadband, room temperature operation, and compact size. In order to achieve broadband operation, the candidate material of the photoconductive antenna PCA usually needs to have an ultra-fast carrier recombination to convert the femtosecond pulsed laser light into a sub-picosecond pulse current to drive the antenna and radiate out the terahertz band electromagnetic waves. Traditional photoconductive materials are mainly based on low-temperature
growth (LT) or transition metal-doped III-V materials under ultra-high vacuum environment through molecular beam epitaxy, which requires precise control of epitaxial conditions and high-temperature annealing process to obtain a high-quality structure. Therefore, complex manufacturing processes and time-consuming properties result in extremely high manufacturing costs, hindering large-scale production and full commercialization of THz photoconductive antennas through mature complementary metal oxide semiconductor processes. Although some teams have proposed
germanium-based THz photoconductive antennas, germanium is an indirect band gap semiconductor. Its bandgap edge is close to the most commonly used 1550 nm laser light, the absorption coefficient is greatly reduced, which in turn reduces the efficiency of generating photocarriers. This makes germanium from integrating with the lightweight and cost-effective 1550nm optical communication band femtosecond laser. This thesis proposes the first prototype of a plasmonic terahertz photoconductor antenna based on germanium-tin alloy. The photoconductor is deposited by thermal evaporation, and the grating structure is used to generate the plasmonic effect, which dramatically improves the optical to THz conversion efficiency. Compared with traditional InGaAs photoconductive terahertz antennas, germanium tin can be highly integrated with the existing silicon process in the process, and it also has better absorption than conventional germanium-based components leading to mass production of THz components.

摘要 i
Abstract ii
Acknowledgments iv
Table of Contents v
Lists of Tables vii
Lists of Figures viii
CHAPTER I 1
Introduction 1
1.1 Motivation 1
1.2 Photoconductive Antenna 2
1.3 Materials of THz Photoconductive Antennas 3
1.4 Thesis Overview 5
CHAPTER II 7
GeSn Growth and Material Characterization 7
2.1 The Formation of GeSn Alloy 7
2.2 Measurement of GeSn Optical and Electrical Properties 8
CHAPTER III 12
Simulation of Plasmonic Gratings and Antenna 12
3.1 Plasmonic Enhancement through Periodic Gratings 12
3.2 Simulation of Bowtie Antenna 14
CHAPTER IV 17
Fabrication Process of GeSn Plasmonic PCA 17
4.1 Plasmonic Structure Fabrication 17
4.2 Antenna Fabrication 20
CHAPTER V 22
Measurement of GeSn Photoconductive Antenna 22
5.1 Optical and THz Measurement Setup 22
5.2 Measurement Result 24
CHAPTER VI 26
Conclusion and Future Work 26
6.1 Conclusion 26
6.2 Future Work 26
Reference 27

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