Daichi Suzuki

GaAs/AlGaAs field-effect transistor for tunable terahertz detection and spectroscopy with built-in signal modulation

We report gate-voltage-controlled signal modulation in terahertz (THz) spectroscopy with a GaAs/AlGaAs two-dimensional electron gas field-effect transistor. By utilizing Landau quantization with magnetic field and Fermi level tuning with the gate voltage, we observed that the amplitude of THz spectroscopic signals was largely modulated with the gate voltage and that the on-off ratio of the modulation reached over 40 dB. This result provides the possibility of a solid-state THz spectrometer with an active modulator.

Thermal Device Design for a Carbon Nanotube Terahertz Camera

Terahertz (THz) wave detectors are increasingly expected to serve as key components of powerful nondestructive and noncontact inspection tools in a large variety of fields. In contrast to conventional THz detectors based on rigid solid materials, we previously developed an uncooled and bendable THz camera based on the THz-induced photothermoelectric effect of carbon nanotube (CNT) array devices and demonstrated omnidirectional THz imaging of three-dimensional curved samples. Although this development opened a pathway to flexible THz electronics, the physical parameters that determine the performance of the CNT THz camera have not been fully investigated. As a result, the thermal device design has not been optimized in terms of the camera sensitivity and spatial resolution. In this work, we studied the underlying mechanism of the THz-induced photothermoelectric effect of the CNT camera and found physical factors related to the detector performance. Through simulation and experiments, we observed that the detection sensitivity and response time strongly depend on the CNT channel width and film thickness. We further identified that the irradiated wave penetration into the CNT film through the electrode materials deteriorates the detection area, which is directly linked to the camera spatial resolution. By utilizing the improved CNT device design fabricated based on these findings, we eliminated undesired signals generated via thermal diffusion and THz wave penetration and achieved higher-sensitivity THz detection and higher imaging resolution compared to our previously reported THz camera. The presented technologies are expected to contribute to future flexible THz imaging applications and will also be applicable to other types of photothermoelectric devices.