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，因为它们有可能成为包括太阳能电池和光电探测器在内的超快光电子器件的构建块。尤其是狄拉克材料，由于其完美的导电表面态和掺杂的可调性，已成为更节能器件的有希望的候选者。然而，要开发功能光电子器件，深入了解这些材料中的载流子传输是必不可少的。太赫兹光谱学提供了一种完美的、非接触、非破坏性的工具，用于检测材料的导电性并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。最近的进展也将这项技术的空间分辨率降到了纳米级。通过将太赫兹光谱和散射型近场光学显微镜(SNOM)相结合，这些材料的电导率和超快载流子输运可以在时间分辨率为1ps和空间分辨率为&lt；30 nm的情况下进行三维绘制。该项目将利用这一技术首次研究III-V纳米线和拓扑绝缘体纳米线中的纳米级载流子传输。它将首次使用表面敏感测量来检测狄拉克材料中奇异的表面电导率响应，而不是大块的。这将提供一种独特的洞察，了解这些材料中控制传输的潜在物理机制，这些机制将直接用于下一代设备(即太赫兹光电探测器)的开发。

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).