To satisfy the demand for broadband and high-sensitivity terahertz detectors, we designed and verified a broadband terahertz detector built with antenna-coupled AlGaN/GaN high-electron-mobility transistors (HEMTs). Eighteen pairs of dipole antennas with different center frequency from 0.24 to 7.4 THz are arrayed into a bow-tie pattern. The corresponding eighteen transistors have common a source and a drain but different gated channels coupled by the corresponding antennas. The photocurrents generated by each gated channel are combined in the drain as the output port. With incoherent terahertz radiation from a hot blackbody in a Fourier-transform spectrometer (FTS), the detector exhibits a continuous response spectrum from 0.2 to 2.0 THz at 298 K and from 0.2 to 4.0 THz at 77 K, respectively. The results agree well with simulations taking into account the silicon lens, antenna and blackbody radiation law. The sensitivity is characterized under coherent terahertz irradiation, the average noise-equivalent power (NEP) is about 188 pW/Hz at 298 K and 19 pW/Hz at 77 K from 0.2 to 1.1 THz, respectively. A maximum optical responsivity of 0.56 A/W and a minimum NEP of 7.0 pW/Hz at 0.74 THz are achieved at 77 K. The blackbody response spectrum is divided by the blackbody radiation intensity to obtain a performance spectrum, which is calibrated by measuring coherence performance from 0.2 to 1.1 THz to evaluate detector performance at frequencies above 1.1 THz. At 298 K, the NEP is about 1.7 nW/Hz at 2.0 THz. At 77 K, the NEP is about 3 nW/Hz at 4.0 THz. For further improvements in sensitivity and bandwidth, high-bandwidth coupling components, smaller series resistance, smaller gate lengths and high-mobility materials need to be considered.

In this article, we report an antenna-coupled AlGaN/GaN high-electron-mobility transistor integrated on a hyper-hemispheric silicon lens for heterodyne detection in a 340 GHz band at room temperature. The responsivity, elevated shot noise, flicker noise, and dynamic source-drain resistance for homodyne and heterodyne detection are characterized and analyzed at different local terahertz (LO) power levels. With a LO power of only −3.9 dBm, the detector offers a conversion loss less than 28 dB and a noise-equivalent power (NEP) about −132 dBm/Hz. A threshold LO power about −5 dBm is identified above which the shot noise becomes the dominant noise source, and the intermediate-frequency response is strongly suppressed. The elevated noise and the saturation in responsivity are found to be closely related to the strong direct-current homodyne current and the charge modulation/accumulation by the LO signal. Possible solutions are discussed to further reduce the NEP and the conversion loss.

In this paper, polystyrene microspheres were firstly prepared by seeded emulsion polymerization, and the uniform monolayer of polystyrene microspheres was prepared on the substrate by the dipping method. Then, polystyrene monolayer film was used as a mask and a low dimensional array structure of gold was prepared by bottom-up self-assembly process. After that, the method of solution etching and annealing was used, and the gold nanoparticle array was post-processed. As a result, gold nanoparticles were recrystallized, with an average diameter of about 50 nm. Subsequently, the semiconductor process was adopted, with focused ion beams induced deposition and electron beam evaporation, and single electron transistors were fabricated, based on self-assembled gold nanoparticles. Finally, the devices were fixed in a liquid helium cryostat and Coulomb blockade was observed at 320 mK. It is a novel fabrication of a single electron transistor based on gold nanoparticle array template and prepared with polystyrene nanospheres.

The foundation for polarization-based terahertz applications is the acquisition of polarization information. To develop an all-electronic terahertz straightforward polarization detection system, in this paper, a terahertz polarization detector based on three antenna-coupled AlGaN/GaN high-electron-mobility transistors (HEMTs) on a single chip is designed and fabricated. The function of the direct polarization detector is proven by measuring the polarization angle of linearly polarized continuous-wave terahertz radiation at 216 GHz. The average deviation and maximum deviation of the measured polarization angle are 3.7 degrees and 10 degrees, respectively. The error comes mainly from the disturbance of the local terahertz field by the interference effect. Simulations locate the sources of interference and guide the further device design and packaging of such kind of direct polarization detectors.

We report a sub-terahertz scattering-type scanning near-field microscope (sub-THz s-SNOM) which uses a 6 mm long metallic tip driven by a quartz tuning fork as the near-field probe. Under continuous-wave illumination by a 94 GHz Gunn diode oscillator, terahertz near-field images are obtained by demodulating the scattered wave at both the fundamental and the second harmonic of the tuning fork oscillation frequency together with the atomic-force-microscope (AFM) image. The terahertz near-field image of a gold grating with a period of 2.3 µm obtained at the fundamental modulation frequency agrees well with the AFM image. The experimental relationship between the signal demodulated at the fundamental frequency and the tip-sample distance is well fitted with the coupled dipole model indicating that the scattered signal from the long probe is mainly contributed by the near-field interaction between the tip and the sample. This near-filed probe scheme using quartz tuning fork can adjust the tip length flexibly to match the wavelength over the entire terahertz frequency range and allows for operation in cryogenic environment.