Abstract-A vertical silicon-graphene-germanium transistor

Chi Liu, Wei Ma, Maolin Chen, Wencai Ren,  Dongming Sun

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https://www.nature.com/articles/s41467-019-12814-1

Graphene-base transistors have been proposed for high-frequency applications because of the negligible base transit time induced by the atomic thickness of graphene. However, generally used tunnel emitters suffer from high emitter potential-barrier-height which limits the transistor performance towards terahertz operation. To overcome this issue, a graphene-base heterojunction transistor has been proposed theoretically where the graphene base is sandwiched by silicon layers. Here we demonstrate a vertical silicon-graphene-germanium transistor where a Schottky emitter constructed by single-crystal silicon and single-layer graphene is achieved. Such Schottky emitter shows a current of 692 A cm−2 and a capacitance of 41 nF cm−2, and thus the alpha cut-off frequency of the transistor is expected to increase from about 1 MHz by using the previous tunnel emitters to above 1 GHz by using the current Schottky emitter. With further engineering, the semiconductor-graphene-semiconductor transistor is expected to be one of the most promising devices for ultra-high frequency operation.

Abstract-Photomechanical meta-molecule array for real-time terahertz imaging

Yongzheng Wen, Delin Jia, Wei Ma, Yun Feng, Ming Liu, Liquan Dong, Yuejin Zhao,  Xiaomei Yu

https://www.nature.com/articles/micronano201771


Real-time terahertz (THz) imaging offers remarkable application possibilities, especially in the security and medical fields. However, most THz detectors work with scanners, and a long image acquisition time is required. Some thermal detectors can achieve real-time imaging by using a focal plane array but have the drawbacks of low sensitivity due to a lack of suitable absorbing materials. In this study, we propose a novel photomechanical meta-molecule array by conveniently assembling THz meta-atom absorbers and bi-material cantilevers together, which can couple THz radiation to a mechanical deflection of the meta-molecules with high efficiency. By optically reading out the mechanical deflections of all of the meta-molecules simultaneously, real-time THz imaging can be achieved. A polyimide sacrificial layer technique was developed to fabricate the device on a glass wafer, which facilitates the transmission of a readout light while the THz wave radiates onto the meta-molecule array directly from the front side. THz images and video of various objects as well as infrared images of the human body were captured successfully with the fabricated meta-molecule array. The proposed photomechanical device holds promise in applications in single and broadband THz as well as infrared imaging.

Abstract-A polarization and angle insensitive terahertz lens based on cascaded complementary metasurfaces

Delin Jia,  Wei Ma,  Yongzheng Wen,  Xiaomei Yu

http://ieeexplore.ieee.org/document/7994451/

In this paper, a three-layer cascaded complementary metasurfaces for complete terahertz (THz) phase control was designed at 3.11 THz. On this basis, a transmissive lens was fabricated and experimentally demonstrated with a focal length of 23 mm and a full width at half maximum (FWHM) of 1.1 mm at the focal plane. Simulations and calculations reveal that the lens is insensitive to incident angle and polarization direction, which is favorable for the development of compact THz imaging and spectroscopy systems.

Abstract-Polarization-independent dual-band terahertz metamaterial absorbers based on gold/parylene-C/silicide structure

Polarization-independent dual-band terahertz metamaterial absorbers based on gold/parylene-C/silicide structure Yongzheng Wen, Wei Ma, Joe Bailey, Guy Matmon, Xiaomei Yu, and Gabriel Aeppli  »View Author Affiliations http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-52-19-4536

We design, fabricate, and characterize dual-band terahertz (THz) metamaterial absorbers with high absorption based on structures consisting of a cobalt silicide (Co-Si) ground plane, a parylene-C dielectric spacer, and a metal top layer. By combining two periodic metal resonators that couple separately within a single unit cell, a polarization-independent absorber with two distinct absorption peaks was obtained. By varying the thickness of the dielectric layer, we obtain absorptivity of 0.76 at 0.76 THz and 0.97 at 2.30 THz, which indicates the Co-Si ground plane absorbers present good performance.

© 2013 Optical Society of America