Continuously tunable Dual Color DFB Laser System for characterization of epitaxial graphene devices at THz frequencies

石墨烯是一种新型材料，在高频电子学和光电子学方面具有广阔的应用前景。有可能，活性石墨烯设备的运行速度可以达到皮秒。然而，据报道，高频晶体管和光电调制器的频率范围不大，仅限于几十千兆赫。太赫兹频率下石墨烯的研究是一项具有挑战性的任务，从根本上讲，从高频辐射与新电子系统相互作用的角度来看，以及在实践中，由于太赫兹范围本身是一个有益的深空观测、安全和健康筛查领域，这一研究的主要目标是建立基于外延石墨烯的远红外和中红外光电子技术的新能力。RHUL在太赫兹技术领域进行了广泛的研究，包括探测器、光源和光学，目标是用于安全和健康筛查的太赫兹成像仪。拥有广泛的技术和专业知识：纳米制造设施、低温实验装置、太赫兹光谱设备、灵敏的太赫兹探测器和光源。直到最近，具有高迁移率的二维EG和超导体的半导体异质结构一直是太赫兹研究的主要材料。我们用一种新材料--外延石墨烯来扩展这一点。外延石墨烯(G/SiC)是在标准的碳化硅晶片上，在Ar气氛中进行热处理得到的。与广泛用于研究的石墨烯薄片相比，G/SiC具有宏观尺寸，并与工业纳米制造技术兼容。碳化硅/石墨与碳化硅衬底有很强的耦合作用，这使得它不同于剥离的石墨烯：它具有不消失的n掺杂，衬底的接近程度影响石墨烯的光学性质，特别是在中红外范围内，碳化硅具有尖锐的吸收边。我们的目标是在新一代设备中利用这些特性，如快速光学开关、发生器和高频辐射探测器。外延石墨烯高频工作的研究已经在与国家物理实验室合作进行中。我们研究了应用于中、远红外探测器和光源的G/SiC的等离子体激元和磁等离子体激元响应。兰开斯特大学一个领先的石墨烯研究小组提供了理论支持。这项工作涉及与瑞典查尔默斯大学和日本东京大学的国际合作。我们建议将我们的设施升级为带宽可调的太赫兹激光器，带宽从0.1太赫兹增加到2太赫兹，精度为0.1 GHz。这个源将提高我们在太赫兹范围内基于G/SiC的器件的光谱能力，并让我们深入了解材料的基本高频特性。该平台将向参与石墨烯研究和开发的英国组织提供。NPL和UCL是该项目的合作伙伴，拥有互补的石墨烯和太赫兹设施。RHUL、NPL和UCL三个组织正在进行一项关于石墨烯高频操作的合作研究。

Graphene is a new material with promising applications in high frequency electronics and optoelectronics. Potentially, active graphene devices can reach operation speed of picoseconds. High frequency transistors and opto- electronic modulators have been reported however in a modest frequency range limited only by tens of gigahertz. A study of graphene at terahertz frequencies, being a challenging task, is of very important, both fundamentally, from the point of interaction of high frequency radiation with a new electronic system, and practically, since terahertz range itself is a rewarding field of deep space observation, security and health screening.The main objective of the proposed research is to build new capabilities of far- and mid- infrared optoelectronics technology based on epitaxial graphene. RHUL carries an extensive research in a field of THz technology, including detectors, sources and optics, with the aim at THz imager for security and health screening. There are in place a wide range of technologies and expertise: nanofabrication facilities, low temperature experimental set up, THz spectroscopic equipment, sensitive THz detectors and sources. Semiconductor hetero-structures with high mobility 2DEG and superconductors were the prime materials of the terahertz research until recently. We expand this with a new material, the epitaxial graphene. The epitaxial graphene (G/SiC) is produced at standard SiC wafer by annealing in Ar atmosphere. In contrast to the flakes of graphene widely used for research, the G/SiC has a macroscopic size, and it is compatible with industrial nanofabrication technology. The SiC/G has a strong coupling to the SiC substrate, which makes it different from the exfoliated graphene: it has a non-vanishing n-doping, proximity of substrate affects optical properties of graphene, particular in the mid- infrared range where SiC has a sharp absorption edge. We aim to utilize these properties in a new generation of devices, like fast optical switches, generators and detectors of high frequency radiation. Study of high frequency operation of epitaxial graphene is in progress already in collaboration with National Physical Laboratory. We investigate plasmon and magneto-plasmon response of the G/SiC in application to mid and far-infrared detectors and sources. Theoretical support is provided from a leading graphene research group at Lancaster University. The work involves international collaboration with Chalmers University in Sweden and Tokyo University in Japan.We propose to upgrade our facilities with tunable THz laser source of bandwidth from 0.1 to 2 THz with accuracy of 0.1 GHz. This source will boost our abilities in spectroscopy of the G/SiC based devices in THz range, as well as give us inside of the fundamental high frequency properties of the material. The platform will be available for the UK organisations involving in graphene research and development. NPL and UCL are partners in the project have a complementary graphene and THz facilities. A collaborative research on high frequency operation of graphene is in progress between three organisations, RHUL, NPL and UCL.