Fabrication of photoconductive antenna with mesa structure for terahertz spectroscopy

太赫兹（THz）电磁波具有1012 Hz量级的频率和100 μ m量级的波长。太赫兹波用于太赫兹时域光谱（THZ-TDS）装置，用于材料和化合物的非破坏性、非侵入性表征。许多材料，包括有机材料、爆炸物、药物化合物和生物制剂，在太赫兹频率下具有不同的特征。在这方面，太赫兹时域成像（THZ-TDI）和光谱（THZ-TDS）不仅对科学家而且对工业利益相关者都非常感兴趣，因为它们在化学传感，医疗诊断和非破坏性质量控制方面具有独特的能力。基于光电导天线（PCA）器件的THz发射机和接收机在很大程度上决定了THz TDS和THz TDI系统的潜在应用和范围。以发射器为例，现有技术的发射器PCA和PCA阵列利用短载流子寿命半导体衬底来产生超快电流，以在飞秒光激光泵浦下产生宽带THz辐射。 在这个项目中，我们将设计，制造和表征三维台面式太赫兹PCA，提供比普通平面PCA更高的效率。PCA将集成到支持公司的产品中，用于测量塑料容器的单层厚度。高性能PCA将能够测量更厚或更多吸收层以及具有更多层的容器。此外，梅萨PCA将工作在激发激光的电信波长（@1550 nm），因此可以利用光纤耦合来给出灵活且紧凑的THz系统。

Terahertz (THz) electromagnetic waves have frequencies of order 10^12 Hz and wavelengths order 100 um. THz waves are used in THz time domain spectroscopy (THZ-TDS) setups for non-destructive, non-invasive characterization of materials and compounds. It has been shown that many materials including organic materials, explosives, pharmaceutical compounds, and biological agents have distinct signatures in the terahertz frequencies. In this regard, terahertz time-domain imaging (THZ-TDI) and spectroscopy (THZ-TDS) are of great interest not only to scientists but also to industrial stake holders for their unique capabilities in chemical sensing, medical diagnosis, and non-destructive quality control. The potential application and scope of THz-TDS & THZ-TDI systems are largely determined by the THz transmitter and receiver that are both based on photoconductive antenna (PCA) device. Taking the transmitter as an example, state of the art transmitter PCAs and PCA arrays utilize short carrier lifetime semiconductor substrate to generate ultrafast current to produce broadband THz radiation under a femtosecond optical laser pump. In this project we will design, fabricate and characterize three-dimensional mesa-like terahertz PCA that offers higher efficiency than the common planar PCA. The PCA will be integrated into the supporting company's product that measures the individual layer thickness of plastic containers. High performance PCA will enable the measurement of thicker or more absorbing layers, as well as containers having more layers. Moreover, the mesa PCA will work at the telecommunication wavelength (@1550 nm) for the excitation laser, and thus fiber-coupling can be utilized to give an agile and compact THz system.