High-Sensitivity RF Choke-Enhanced Dipole Antenna-Coupled Nb5N6 THz Detector

In this study, we demonstrate an Nb5N6 terahertz (THz) detector with radio frequency (RF) choke-enhanced dipole antenna structure for 0.3 THz detection. The maximum electric field intensity of 218 V/m is obtained by optimizing the parameters of the dipole antenna with RF choke. Compared to a dipole antenna without RF choke, the electric field intensity of that with RF choke is improved by 2.6 times. The RF choke-enhanced dipole antenna-coupled Nb5N6 THz detector is fabricated and characterized. The measured maximum responsivity of the detector is 1100 V/W at 0.308 THz, and the corresponding noise equivalent power (NEP) is 6.4 × 10–12 W/Hz1/2. The measured response time of the Nb5N6 THz detector is as low as 8.46 μs. Furthermore, the Nb5N6 THz detector is applied to a homemade THz transmission imaging system for demonstrating its performance. The THz imaging results of a blade and access card show that the contrast of the blade image is sharp and the components hidden within the access card are clearly visible. This indicates that the Nb5N6 THz detector can be used in THz imaging, particularly in THz active imaging, which will have greater application prospects.

A Terahertz Detector Based on Double-Channel GaN/AlGaN High Electronic Mobility Transistor

A double-channel (DC) GaN/AlGaN high-electron-mobility transistor (HEMT) as a terahertz (THz) detector at 315 GHz frequency is proposed and fabricated in this paper. The structure of the epitaxial layer material in the detector is optimized, and the performance of the GaN HEMT THz detector is improved. The maximum responsivity of 10 kV/W and minimum noise equivalent power (NEP) of 15.5 pW/Hz0.5 are obtained at the radiation frequency of 315 GHz. The results are comparable to and even more promising than the reported single-channel (SC) GaN HEMT detectors. The enhancement of THz response and the reduction of NEP of the DC GaN HEMT detector mainly results from the interaction of 2DEG in the upper and lower channels, which improves the self-mixing effect of the detector. The promising experimental results mean that the proposed DC GaN/AlGaN HEMT THz detector is capable of the practical applications of THz detection.

Terahertz Raman Measurements Using a Spatial Heterodyne Raman Spectrometer

We propose a method of measuring the terahertz (THz) Raman spectra of a material. As Raman spectroscopy is a measurement of the relative frequency spectrum relative to the frequency of the excitation source, it is not necessary to use an expensive THz source and THz detector. Instead, an ultraviolet, visible, or infrared excitation source and corresponding detector can be used. A combination of prisms and gratings is used to widen the field of view at high resolution. The resolution of the system is 4.945 cm−1 (0.149 THz), and the spectral range is 2531.84 cm−1 (75.963 THz). We measured the THz Raman spectra of solid powder, aqueous solutions, and mixtures, and studied the effects of environment, container material, and time of measurement on the spectra. The results show that the system is not significantly affected by interference from the water environment and has good stability and repeatability. This method can be applied in many fields such as material detection and environmental protection.

Fabrication of Graphene Nanomesh FET Terahertz Detector

High sensitivity detection of terahertz waves can be achieved with a graphene nanomesh as grating to improve the coupling efficiency of the incident terahertz waves and using a graphene nanostructure energy gap to enhance the excitation of plasmon. Herein, the fabrication process of the FET THz detector based on the rectangular GNM (r-GNM) is designed, and the THz detector is developed, including the CVD growth and the wet-process transfer of high quality monolayer graphene films, preparation of r-GNM by electron-beam lithography and oxygen plasma etching, and the fabrication of the gate electrodes on the Si3N4 dielectric layer. The problem that the conductive metal is easy to peel off during the fabrication process of the GNM THz device is mainly discussed. The photoelectric performance of the detector was tested at room temperature. The experimental results show that the sensitivity of the detector is 2.5 A/W (@ 3 THz) at room temperature.

Novel Broadband Slot-Spiral Antenna for Terahertz Applications

We report a novel broadband slot-spiral antenna that can be integrated with high-electron-mobility transistor (HEMT) terahertz (THz) detectors. The effect of various antenna parameters on the transmission efficiency of the slot-spiral structure at 150–450 GHz is investigated systematically. The performances of the slot-spiral antenna and the spiral antenna both integrated with HEMTs are compared. The results show that the slot-spiral structure has a better transmission and miniaturization capability than the spiral structure. A formula for the responsivity is derived based on the transmission line principle and antenna theory, and results show that the detector responsivity is correlated with the antenna absorptivity. Additionally, guidelines for HEMT THz detector design are proposed. The results of this study indicate the excellent application prospects of the slot-spiral antenna in THz detection and imaging.