Chip-Type Near-Field Terahertz Spectroscopic Imagers and Their Application to a Study of Quantum Transport

Abstract

Near-field terahertz (THz) spectroscopic imaging, which enables sub-wavelength analysis, is a powerful method for investigating nano- and micro-scale objects such as nanomaterials, polymers, cells, and biomolecules. However, near-field imaging in the THz region remains to be fully explored, compared to other frequency regions. This review explains our chip-type near-field THz spectroscopic imaging technology. We develop a collection-mode near-field THz imager, which is based on an evanescently coupled THz sensor with a two-dimensional electron gas. The utilization of frequency-selective THz detection makes it possible to obtain near-field THz images in separate frequency bands. With this technology, we perform cryogenic near-field THz-emission imaging without external THz sources, and visualize the spatial distribution of THz radiation associated with electron injection from a source electrode in a semiconductor device. Finally, a graphene-based THz detector with wide-band frequency-tunability is presented, in which the detection mechanism is based on Landau-level formation of Dirac fermions of the graphene. This device is promising as a wide-band near-field THz spectroscopic imager.