Nanoscale imaging and spectroscopy of charge carrier distribution with terahertz and mid infrared near-field nanoscopy

We perform terahertz (THz) and mid infrared nanoscopy to probe and quantify charge carriers in doped semiconductor surfaces and doped Si nanowires at the nanoscale. We introduce hyperspectral THz nano-imaging by combining scattering-type scanning near-field optical microscopy (s-SNOM) with THz time-domain spectroscopy (TDS). We describe the technical implementations that enabled this achievement and demonstrate its performance. Combination of nanoscale spectroscopy and Drude model allows for measuring—noninvasively and without the need for Ohmic contacts—the local mobile carrier concentration of the differently doped semiconductor areas.