Development of the next generation of THz devices: detectors to modulators

太赫兹(THz)频率器件的发展对太赫兹科学技术的进步至关重要。太赫兹光谱区域对许多应用特别有吸引力；众所周知，药物或爆炸物在太赫兹光谱中呈现光谱指纹，而相反，塑料材料对这种辐射是透明的，这在安全扫描中具有独特的应用。此外，不同的化学试剂或分子吸收在中/远红外；常见的污染物，如二氧化氮，或温室气体，如一氧化碳，二氧化碳，或甲醇，在这一光谱区域呈现振转和转动跃迁，从而有助于环境监测。开发高效、快速的THz探测器和开关/调制器对许多此类应用至关重要。已经报道了一些在半导体器件中利用二维电子气(2DEG)的检测机制。我们团队最近开发了一种新的栅极偏置器件结构，使2DEG不均匀，从而使THz光响应不是通过利用传统的电子加热实现的，而是通过光子辅助隧道效应实现的。这种检测机制允许利用这一过程固有的超快响应。人们将探索更复杂的探测器结构，不仅旨在优化天线设计以提高THz检测灵敏度，而且还将开发用于THz成像应用的探测器阵列。利用一种新的量子材料--拓扑绝缘体(TI)--的THz应用具有巨大的潜力。拓扑材料的一个令人兴奋的性质是通过拓扑表面态的无耗散表面输运。从理论上讲，光响应可以扩展到太赫兹光谱范围，潜在的SNR将大大超过传统的光探测方法。一个有趣的设备架构将是基于TI的太赫兹光电探测器/调制器。这将使太赫兹照明能够主动控制拓扑相和非拓扑相之间的转换，从而改变设备的传输特性。这将使太赫兹光子能够充当一个开关，以光学方式打开/关闭拓扑面状态(TSS)。

The development of devices operating in the terahertz (THz) frequency is of paramount importance for the progress of THz science and technology. The THz spectral region is particularly appealing for many applications; it is widely known that drugs or explosives present spectral fingerprints in the THz, while, conversely, plastic material are transparent to this radiation, which uniquely finds application in security scanning. Moreover, diverse chemical agents, or molecules are absorbing in the mid/far infrared; common pollutants, such as nitrogen dioxide, or greenhouse gases, such as carbon monoxide, dioxide, or methanol, present ro-vibrational and rotational transitions in this spectral region, thus lending itself to environmental monitoring.The development of efficient and fast THz detectors and switches/modulators is critical to a number of these applications. A number of detection mechanisms utilising two-dimensional electron gases (2DEGs) in semiconductor devices have been reported. Our group has recently developed a novel gate biasing device architecture that makes the 2DEG non-uniform such that THz photo-response is achieved not by exploiting conventional electron heating but from photon-assisted tunnelling. This detection mechanism allows for the exploitation of the inherent ultra fast response of this process. More complex detector architectures will be explored that not only aim to optimise the antenna design to improve THz detection sensitivity, but also the development of detector arrays for THz imaging applications.THz applications utilising a new class of quantum materials known as Topological Insulators (TI) has great potential. One exciting property of topological materials is dissipationless surface transport, through topological surface states (TSS). Theoretically the photo-response can be extended to the THz spectral regime, with a potential SNR that would largely exceed those of conventional photo-detecting approaches. An interesting device architecture would be a TI based THz photodetector/modulator. This would enable THz illumination to actively control the transition between topological and non-topological phases, altering the transport characteristics of the device. This would enable THz photons to act as a 'switch' to turn the topological surface state (TSS) on/off optically.