Terahertz nanospectroscopy of plasmon polaritons for the evaluation of doping in quantum devices

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