Exploring the nanoscale optoelectronic properties of low-dimensional materials via terahertz spectroscopy and near-field terahertz microscopy

低维半导体材料在纳米技术领域极具吸引力，因为它们具有作为超快光电器件（包括太阳能电池和光电探测器）的构件的潜力。特别是狄拉克材料，由于其完美的导电表面态和掺杂的介电常数，已经成为更节能器件的有希望的候选者。然而，为了开发功能性光电器件，深入了解这些材料中的载流子输运是必不可少的。太赫兹光谱提供了一种完美的、非接触的、非破坏性的工具，用于检查材料的电导率和提取关键的传输参数，如迁移率、载流子寿命和非本征载流子浓度。最近的进展也将这种技术的空间分辨率推到了纳米级。通过将太赫兹光谱与散射型近场光学显微镜（SNOM）相结合，这些材料中的电导率和超快载流子输运可以以<1 ps的时间分辨率和<30 nm的空间分辨率进行3D映射。本计画将利用此技术进行第一次III-V族奈米线与拓扑绝缘体奈米线奈米载子输运之研究。它将采用表面敏感的测量，以检查奇特的表面电导率响应狄拉克材料独立于散装的第一次。这将提供一个独特的洞察力的基础物理机制，管理这些材料中的运输，将直接进入下一代设备（即太赫兹光电探测器）的发展。

Low-dimensional semiconductor materials are extremely attractive in the field of nanotechnology owing to their potential as building blocks for ultrafast optoelectronic devices, including solar cells and photodetectors. Dirac materials, in particular, have emerged as promising candidates for more energy-efficient devices, owing to their perfectly-conducting surface states and doping tuneability. However, to develop functional optoelectronic devices, an in-depth understanding of carrier transport in these materials is essential. Terahertz spectroscopy provides a perfect, non-contact, non-destructive tool for examining the electrical conductivity of a material and extracting key transport parameters, such as mobility, carrier lifetime and extrinsic carrier concentration. Recent advances have also pushed the spatial resolution of this technique down to the nanoscale. By combining terahertz spectroscopy with scattering-type near-field optical microscopy (SNOM), electrical conductivity and ultrafast carrier transport in these materials can be mapped in 3D with <1ps temporal resolution and <30nm spatial resolution. This project will exploit this technique to conduct the first investigation of nanoscale carrier transport in III-V nanowires and topological insulator nanowires. It will employ surface-sensitive measurements to examine the exotic surface conductivity response in Dirac materials independently from the bulk for the first time. This will provide a unique insight into the underlying physical mechanisms governing transport in these materials that will directly feed into development of next-generation devices (namely terahertz photodetectors).