Graphene Thermoelectric THz Direct and Heterodyne Detectors

太赫兹或太赫兹辐射的检测，是频率介于微波和红外线之间的电磁波，可用于广泛的应用，包括调查宇宙中恒星和星系的形成和演化，分析制药业药丸和药片上涂层的厚度，区分癌细胞和健康组织，发现制造缺陷，进行非破坏性质量控制分析，识别衣服下隐藏的物体，以及远程嗅探爆炸物和非法药物。太赫兹技术研究的一个长期目标是开发一种多像素太赫兹“相机”，它可以从物体产生太赫兹辐射的图像，类似于通常使用的用可见光拍照的数码相机。由于典型室温设备的灵敏度和速度有限，目前太赫兹成像需要使用高功率、相干的太赫兹照明源。精心设计的太赫兹探测器可以达到高灵敏度和快速。然而，这类设备通常需要冷却到低温。在这里，石墨烯，一个碳原子的单原子层，将被用来制造在室温下工作的紧凑和高性能的太赫兹探测器。具体地说，石墨烯将被加工成热电偶，可以快速有效地检测由于太赫兹辐射吸收而产生的加热效应。该项目经过充分优化的设备预计将达到与必须用液氦冷却的现有系统相当的性能，为开发紧凑型室温太赫兹相机铺平道路，该相机可以记录环境的热像，而不需要强烈的太赫兹光源。这一研究项目将在二维材料、纳米科学、技术与工程、光学、太赫兹仪器和凝聚态物理方面为来自不同社会经济背景和代表性社区的研究生、本科生和高中生提供独特的跨学科科学教育和培训计划。最近对石墨烯的密集电学和光学研究将这种材料推到了太赫兹研究的前沿，因为这种原子薄的晶体具有高迁移率、弱电子-声子耦合、可调的宽带光学响应和微小的比热。这项拟议的研究旨在利用这些独特的性质，制造高质量的石墨烯-氮化硼原子栈，通过热电机制检测THz辐射：THz辐射加热石墨烯中的电子，同时保持晶格与环境的热平衡；热电子的扩散产生温度梯度，在具有破缺镜像对称性的器件中，该温度梯度产生热电电压信号。这种探测机制可以有效地避免砷化镓肖特基势垒二极管和半导体等离子体探测器中常见的高频性能衰减，并由于石墨烯？S较小的电子热容而提供非常快的响应。太赫兹探测器将通过集成电路天线和硅透镜与入射辐射耦合。该项目将开发：1.高响应度、快速、低噪声当量功率的石墨烯热电直接探测器；2.低本振功率要求和室温工作的高灵敏度石墨烯热电外差探测器。将评估在未来的太赫兹阵列成像器中使用外差探测器的潜力。除了潜在的应用，这些结果有望提供关键信息来阐明相关物理过程的潜在机制，包括热电过程的速度、热电子的产生和驰豫以及电荷密度和阻抗分布对热电电压的影响。

Detection of terahertz or THz radiation, the electromagnetic waves with frequencies in-between that of microwaves and infrared light, is useful for a wide range of applications, including investigating the formation and evolution of stars and galaxies in the universe, analyzing the thickness of coatings on pills and tablets in the pharmaceutical industry, distinguishing cancer cells from healthy tissues, spotting manufacturing flaws for non-destructive quality-control analysis, identifying concealed objects under clothing, and sniffing out explosives and illegal drugs remotely. A long-standing objective of THz technology research has been to develop a multi-pixel THz "camera" that can produce images of the THz radiation from an object, similar to the commonly-used digital cameras that take pictures with visible light. Because of the limited sensitivity and speed for typical room temperature devices, THz imaging presently requires the use of a high power, coherent, THz illumination source. Meticulously engineered THz detectors can reach high sensitivity and fast speed. However such devices typically need to be cooled down to cryogenic temperatures. Here graphene, a single atomic sheet of carbon atoms, will be used to make compact and high performance THz detectors operating at room temperature. Specifically graphene will be processed into a thermocouple that can rapidly and efficiently sense the heating effects due to THz radiation absorption. Fully optimized devices from the project are expected to reach a performance equivalent to existing systems that have to be cooled down with liquid helium, paving way for developing a compact room temperature THz camera that can record thermal images of the environment without the need for an intense THz light source. This research project will provide a unique inter-disciplinary scientific education and training program in two dimensional materials, nano science, technology and engineering, optics, THz instrumentation and condensed matter physics to graduate, undergraduate and high school students from diverse socio-economic backgrounds and under-represented communities.Recent intense electrical and optical studies of graphene have pushed the material to the forefront of THz research due to the atomically thin crystal's high mobility, weak electron-phonon coupling, tunable broadband optical response and minute specific heat. The proposed research seeks to take advantage of these unique properties and fabricate high quality graphene-boron nitride atomic stacks to detect THz radiation through a thermoelectric mechanism: THz radiation heats up electrons in graphene while keeping the lattice in thermal equilibrium with the environment; the diffusion of hot electrons creates a temperature gradient which, in a device with broken mirror symmetry, generates a thermoelectric voltage signal. This detection mechanism can effectively circumvent performance roll off at high THz frequencies, commonly encountered in gallium arsenide Schottky barrier diode and semiconductor plasmon detectors, and provide very fast response due to graphene?s small electron heat capacity. The THz detectors will be coupled to the incoming radiation through an integrated circuit antenna and a silicon lens. The project will develop: 1. graphene thermoelectric direct detectors with high responsivity, fast speed and low noise equivalent power; 2. graphene thermoelectric heterodyne detectors reaching high sensitivity with low local oscillator power requirement and room temperature operation. The potential for employing the heterodyne detectors in future THz array imagers will be evaluated. In addition to potential applications, the results are expected to provide key information to elucidate the underlying mechanism of the relevant physical processes, including the speed of the thermoelectric process, generation and relaxation of hot electrons, as well as the impacts of the charge density and impedance profile on the thermoelectric voltage.