Terahertz (THz) waves are a highly sensitive probe of free carrier concentrations in semiconducting materials. However, most experiments operate in the far-field, which precludes the observation of nanoscale features that affect the material response. Here, we demonstrate the use of nanoscale THz plasmon polaritons as an indicator of surface quality in prototypical quantum devices properties. Using THz near-field hyperspectral measurements, we observe polaritonic features in doped silicon near a metal-semiconductor interface. The presence of the THz surface plasmon polariton indicates the existence of a thin film doped layer on the device. Using a multilayer extraction procedure utilising vector calibration, we quantitatively probe the doped surface layer and determine its thickness and complex permittivity. The recovered multilayer characteristics match the dielectric conditions necessary to support the THz surface plasmon polariton. Applying these findings to superconducting resonators, we show that etching of this doped layer leads to an increase of the quality factor as determined by cryogenic measurements. This study demonstrates that THz scattering-type scanning near-field optical microscopy (s-SNOM) is a promising diagnostic tool for characterization of surface dielectric properties of quantum devices.

中文翻译：

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等离子体激元的太赫兹纳米光谱学用于评估量子器件中的掺杂

太赫兹 (THz) 波是半导体材料中自由载流子浓度的高度灵敏探测器。然而，大多数实验在远场进行，这排除了观察影响材料响应的纳米级特征。在这里，我们展示了使用纳米级太赫兹等离子体激元作为原型量子器件特性中表面质量的指标。使用 THz 近场高光谱测量，我们观察了金属-半导体界面附近掺杂硅中的极化子特征。太赫兹表面等离子体激元的存在表明器件上存在薄膜掺杂层。使用利用矢量校准的多层提取程序，我们定量探测掺杂表面层并确定其厚度和复介电常数。恢复的多层特性与支持太赫兹表面等离子体激元所需的介电条件相匹配。将这些发现应用于超导谐振器，我们表明蚀刻该掺杂层会导致品质因数的增加，这由低温测量确定。这项研究表明，太赫兹散射型扫描近场光学显微镜 (s-SNOM) 是一种很有前途的诊断工具，可用于表征量子器件的表面介电特性。