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

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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).