Abstract-Smaller antenna-gate gap for higher sensitivity of GaN/AlGaN HEMT terahertz detectors

Applied Physics Letters

Zhipeng Zhang, Xiang Li, Hua Qin, Jinfeng Zhang, Xinxing Li, Yang Shangguan, Lin Jin, Yunfei Sun, V. V. Popov,

(a) Schematic diagram of the GaN/AlGaN HEMT detector including the measurement circuit. (b) Zoom-in view of the central active region.

https://aip.scitation.org/doi/abs/10.1063/1.5142436

We report an attempt to improve the sensitivity of terahertz detection based on self-mixing in antenna-coupled field-effect transistors by enhancing the field-effect factor and the antenna factor with a reduced gate length and a reduced antenna-gate gap, respectively. An optical noise equivalent power (NEP) of 3.7 pW/Hz⎯⎯⎯⎯⎯√$3.7\hspace{0.17em}\text{pW}/\sqrt{\text{Hz}}$ at 0.65 THz was achieved in a GaN/AlGaN high-electron-mobility transistor (HEMT) with a gate length of 300 nm and an antenna-gate gap of 200 nm at room temperature. It was found that the antenna factor was inversely proportional to the antenna-gate gap, and the responses upon coherent/incoherent terahertz irradiation were well described by the self-mixing model. To fill the NEP gap of 0.1−1 pW/Hz⎯⎯⎯⎯⎯√$0.1-1\hspace{0.17em}\text{pW}/\sqrt{\text{Hz}}$ between room-temperature and cryogenic detectors by HEMT-based detectors at room temperature, impedance match needs to be carefully considered.

The authors acknowledge support from the National Natural Science Foundation of China (Nos. 61771466, 61775231, and 61975227), the Youth Innovation Promotion Association CAS (No. 2017372), the Six Talent Peaks Project of Jiangsu Province, China (XXRJ-079), and the Russian Foundation for Basic Research (No. 17-52-53063). The work in the Kotelnikov IRE RAS was carried out within the framework of the state task.

Abstract-Terahertz frequency spectrum analysis with a nanoscale antiferromagnetic tunnel junction

Journal of Applied Physics

Sulymenko,  S. Louis, J. Li,  R. S. Khymyn, E. Bankowski,  T. Meitzler,  V. S. Tyberkevych,  A. N. Slavin,  O. V. Prokopenko,

(a) Pt/AFM/MgO/Pt antiferromagnetic tunnel junction (ATJ). The driving dc current Idrive(t)$I_{\mathrm{drive}}(t)$ flowing in the bottom Pt layer of an ATJ generates the transverse spin current ISH$I_{\mathrm{SH}}$ flowing into the AFM layer, which excites the TF rotation of magnetization of the AFM sublattices and, consequently, the TF variations of the junction resistance R(t)$R(t)$. When a TF signal with power Ps$P_s$ and frequency fs$f_s$ is supplied to the junction, its action results in the generation of voltage Uatj$U_{\mathrm{atj}}$ across the whole structure. (b) A simplified equivalent electric scheme of the ATJ-based detector connected through an ideal bias tee to a source of an external TF signal.

https://aip.scitation.org/doi/10.1063/1.5140552

A method to perform spectrum analysis on low power signals between 0.1$0.1$ and 10 THz is proposed. It utilizes a nanoscale antiferromagnetic tunnel junction (ATJ) that produces an oscillating tunneling anisotropic magnetoresistance, whose frequency is dependent on the magnitude of an evanescent spin current. It is first shown that the ATJ oscillation frequency can be tuned linearly with time. Then, it is shown that the ATJ output is highly dependent on matching conditions that are highly dependent on the dimensions of the dielectric tunneling barrier. Spectrum analysis can be performed by using an appropriately designed ATJ, whose frequency is driven to increase linearly with time, a low pass filter, and a matched filter. This method of THz spectrum analysis, if realized in the experiment, will allow miniaturized electronics to rapidly analyze low power signals with a simple algorithm. It is also found by simulation and analytical theories that for an ATJ with a 0.09μm2$0.09\mu {\mathrm{m}}^2$ footprint, spectrum analysis can be performed over a 0.25THz$0.25\mathrm{THz}$ bandwidth in just 25 ns on signals that are at the Johnson–Nyquist thermal noise floor.

Abstract-Study of 2,4-D Spectral Characteristics and Its Detection in Zizania Latifolia Using Terahertz Time-Domain Spectroscopy

Pengcheng Nie, Chengyong Cai,  Fangfang Qu, Lei Lin, Tao Dong, Yong He,

https://www.mdpi.com/2076-3417/9/11/2248

2,4-Dichlorophenoxyacetic acid (2,4-D) is a common plant growth regulator, which can remain in food and, with long-term consumption, threaten human health. Therefore, it is necessary to propose an effective detection method. Terahertz time-domain spectroscopy technique (THz-TDS) has good advantages in the quantitative and qualitative analysis of most biomolecules due to its rich fingerprint characteristics. In this paper, density functional theory (DFT) was applied to geometry optimization and frequency vibration calculation of 2,4-D, and THz-TDS was used to quantitatively detect 2,4-D in Zizania latifolia. The results showed that there were three characteristic absorption peaks of 2,4-D at 1.36, 1.60, and 2.38 THz, respectively, and the theoretical spectra were in good consistency with experimental spectra, with slight discrepancies. Additionally, the absorption peak at 1.36 THz had the best absorption characteristics and was chosen as the main peak for 2,4-D quantitative analysis. It was demonstrated that the limits of detection (LOD) of 2,4-D in Zizania latifolia were found to be as low as 5%, the absorbance intensity at 1.36 THz showed a good linear relationship (R² = 0.9854) with 2,4-D concentration from 5% to 30%, and the recovery was 93.29%–98.75%. Overall, this work enriched the fingerprint database of pesticide molecules on the basis of terahertz spectroscopy and could provide a technical support for the detection of 2,4-D in food by terahertz spectroscopy

Abstract-A high-performance broadband terahertz absorber based on sawtooth-shape doped-silicon

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Liang-Hui Du1,2,a), Jiang Li1,2, Zhao-Hui Zhai1,2, Kun Meng1,2, Qiao Liu1,2, Sen-Cheng Zhong1,2, Ping-Wei Zhou1,2, Li-Guo Zhu1,2,b), Ze-Ren Li1,2 and Qi-Xian Peng1,2

a) Electronic mail: Lianghui_Du@163.com

b) Electronic mail: zhuliguo@tsinghua.org.cn

AIP Advances 6, 055112 (2016); http://dx.doi.org/10.1063/1.4950800

http://scitation.aip.org/content/aip/journal/adva/6/5/10.1063/1.4950800?TRACK=RSS

Perfect absorbers with broadband absorption of terahertz (THz) radiation are promising for applications in imaging and detection to enhance the contrast and sensitivity, as well as to provide concealment. Different from previous two-dimensional structures, here we put forward a new type of THz absorber based on sawtooth-shape doped-silicon with near-unit absorption across a broad spectral range. Absorbance over 99% is observed numerically from 1.2 to 3 THz by optimizing the geometric parameters of the sawtooth structure. Our absorbers can operate over a wide range of incident angle and arepolarization insensitive. The underlying mechanisms due to the combination of an air-cavity mode and mode-matching resonance on the air-sawtooth interface are analyzed in terms of the field patterns and electromagnetic power loss features.

Abstract-Free-Standing Metasurfaces for High-Efficiency Transmitarrays for Controlling Terahertz Waves

1. Shuo Liu^1,2, 
2. Qiang Cheng^1,3, 
3. Quan Xu⁴,
4. Tian Qi Wang^1,2, 
5. Liang Liang Du⁴, 
6. Kang Luan^1,2, 
7. Yue Hong Xu⁴, 
8. Di Bao^1,2, 
9. Xiao Jian Fu^1,2, 
10. Jia Guang Han⁴, 
11. Wei Li Zhang^3,4 and
12. Tie Jun Cui^1,3,*

Article first published online: 11 DEC 2015

DOI: 10.1002/adom.201500519

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

http://onlinelibrary.wiley.com/doi/10.1002/adom.201500519/abstract;jsessionid=1E8BB761E0D01A393F30C1F518B17754.f01t04?userIsAuthenticated=false&deniedAccessCustomisedMessage=

An ultrathin free-standing metasurface is proposed to bend the normally incident terahertz wave to an anomalous direction, or to focus plane wave to a point, with high efficiency. The flexibility and endurable nature of the proposed transmitarray make it a promising candidate for various THz applications such as time-domain system or THz imaging devices.

Abstract-Polarization-dependent thin-film wire-grid reflectarray for terahertz waves

Tiaoming Niu^1,2, Aditi Upadhyay³, Withawat Withayachumnankul^1,4, Daniel Headland¹, Derek Abbott¹, Madhu Bhaskaran³, Sharath Sriram³ andChristophe Fumeaux^1,a)
 HIDE AFFILIATIONS
1 School of Electrical and Electronic Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia
2 School of Information Science and Engineering, Lanzhou University, Lanzhou 730000, People's Republic of China
3 Functional Materials and Microsystems Research Group, RMIT University, Melbourne, Victoria 3001, Australia
4 Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1-S9-3, Ookayama, Meguro-ku, Tokyo 152-8552, Japan

A thin-film polarization-dependent reflectarray based on patterned metallic wire grids is realized at 1 THz. Unlike conventional reflectarrays with resonant elements and a solid metal ground, parallel narrow metal strips with uniform spacing are employed in this design to construct both the radiation elements and the ground plane. For each radiation element, a certain number of thin strips with an identical length are grouped to effectively form a patch resonator with equivalent performance. The ground plane is made of continuous metallic strips, similar to conventional wire-grid polarizers. The structure can deflect incident waves with the polarizationparallel to the strips into a designed direction and transmit the orthogonal polarizationcomponent. Measured radiation patterns show reasonable deflection efficiency and highpolarization discrimination. Utilizing this flexible device approach, similar reflectarray designs can be realized for conformal mounting onto surfaces of cylindrical or spherical devices for terahertz imaging and communications.