Associate Professor, Quantum Nano-electronics Research Centre, Tokyo Institute of Technology
Sensing and imaging with terahertz (THz) waves are an active area in modern optical science and technology. The advantageous properties of terahertz (THz) waves, such as the important energy spectrum in the meV range, enable various applications of imaging and spectroscopy. However, since the THz region is located between electronic and photonic bands, even basic components like detector and source have not been fully established, compared to other frequency regions. The THz wave also has the problem of low imaging resolution, which results from a much longer wavelength than that of the visible light. By employing nanoelectronics materials and devices based on a carbon nanotube (CNT), graphene, and a two-dimensional electron gas (2DEG) in a semiconductor heterostructure, we developed novel types of THz sensing and imaging devices:
1) THz-photon sensor with a CNT/2DEG hybrid device
In order to achieve highly sensitive THz detection, we studied THz response of a CNT/2DEG hybrid device. The utilization of this device structure enabled the detection of THz photons.
2) Near-field THz imager with sub-wavelength resolution
The development of near-field THz imaging had been hindered by the lack of high transmission wave line and the low sensitivity of commonly used detectors. We produced a newly designed THz near-field imager, in which all the components: an aperture, a probe, and a detector are integrated on one semiconductor chip. The development of this device allowed us to achieve sub-wavelength resolution for the wavelength of 100-300 µm. Electronic and molecular structures of quantum semiconductors, plasmonic devices, and polymers were visualized with this imaging device.
3) Wide-band, frequency-selective THz spectrometer with graphene
We succeeded in observing THz photoconductivity of Dirac fermions in graphene, ranging over a wide frequency band of 0.8-33 THz. This result demonstrated that the graphene device works as a wide-band, frequency-selective THz spectrometer. We also imaged potential fluctuations in the graphene device, suggesting the strong relation to the THz photoconductivity.
Our technologies and findings provided new insights into low-energy and low-frequency dynamics in physics and chemistry.