Bo Zhang

Abstract: With the exponential growth of the data traffic in wireless communication systems, terahertz (THz) frequency band is envisioned as a promising candidate to support ultra-broadband for future beyond fifth generation (5G), bridging the gap between millimeter wave (mmWave) and optical frequency ranges. The purpose of this paper is to provide a comprehensive literature review on the development towards THz communications and presents some key technologies faced in THz wireless communication systems. Firstly, despite the substantial hardware problems that have to be developed in terms of the THz solid state superheterodyne receiver, high speed THz modulators and THz antennas, the practical THz channel model and the efficient THz beamforming are also described to compensate for the severe path attenuation. Moreover, two different kinds of lab-level THz communication systems are introduced minutely, named a solid state THz communication system and a spatial direct modulation THz communication system, respectively. The solid state THz system converts intermediate frequency (IF) modulated signal to THz frequency while the direct modulation THz system allows the high power THz sources to input for approving the relatively long distance communications. Finally, we discuss several potential application scenarios as well as some vital technical challenges that will be encountered in the future THz communications.

Abstract: The past few decades have witnessed a substantial increase in terahertz (THz) research. Utilizing THz waves to transmit communication and imaging data has created a high demand for phase and amplitude modulation. However, current active THz devices, including modulators and switches, still cannot meet THz system demands. Double-channel heterostructures, an alternative semiconductor system, can support nanoscale two-dimensional electron gases (2DEGs) with high carrier concentration and mobility and provide a new way to develop active THz devices. In this Letter, we present a composite metamaterial structure that combines an equivalent collective dipolar array with a double-channel heterostructure to obtain an effective, ultrafast, and all-electronic grid-controlled THz modulator. Electrical control allows for resonant mode conversion between two different dipolar resonances in the active device, which significantly improves the modulation speed and depth. This THz modulator is the first to achieve a 1 GHz ...

Abstract: A novel silicon-on-insulator (SOI) high-voltage device structure with double-sided trenches on the buried oxide layer (DT SOI) is proposed and its breakdown characteristics are investigated theoretically and experimentally in this letter. Theoretically, the charges implemented in the DTs, whose density changes with the drain voltage, increase the electric field in the buried layer and modulate the electric field in the drift region, which results in the enhancement of the breakdown voltage (BV). Experimentally, the BV of 730 V is obtained for the first time in SOI LDMOS with DT on 20-mum SOI layer and 1- mum buried oxide layer

Abstract: An AlGaN/GaN-on-Si lateral power diode with recessed metal/Al2O3/III-nitride (MIS)-gated ohmic anode for improved forward conduction and reverse blocking has been realized. The low onset voltage of $\sim 0.6$ V with good uniformity for the fabricated 189 devices is obtained. In comparison with the conventional Schottky diode the specific ON-resistance ( $R_{\mathrm {\mathbf {\mathrm{{\scriptscriptstyle ON}},SP}}})$ was reduced by 51% in a device with anode-to-cathode spacing ( $L_{\mathrm {\mathbf {AC}}})$ of 5 $\mu \text{m}$ . The incorporation of high- $k$ dielectric in the recessed gate region enabling two-order lower reverse leakage comparing with the conventional device, leading to a high breakdown voltage over 1.1 kV at leakage current as low as 10 $\mu \text{A}$ /mm in device with $L_{\mathrm {\mathbf {AC}}}=20~\mu \text{m}$ . The strong reverse blocking over 600 V was still achieved at 150 °C. The proposed diode is compatible with GaN normally $\mathbf {\mathrm{{\scriptstyle OFF}}}$ MIS high-electron-mobility transistors, revealing its potential for highly efficient GaN-on-Si power ICs.

Abstract: A new silicon-on-insulator (SOI) power MOSFET structure is proposed, in which buried oxide step structure (BOSS) is replaced by a buried oxide double step (BODS). Numerical simulations are performed to demonstrate that higher breakdown voltages are obtained resulting from a higher electric-field peak introduced near the BODS, and higher impurity concentration is depleted due to thin-film SOI than that in the conventional SOI and BOSS structure.

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Abstract: Metamaterials are composed of periodic subwavelength metal/dielectric structures that resonantly couple to the electric and/or magnetic components of the incident electromagnetic fields, exhibiting properties that are not found in nature. This class of micro- and nano-structured artificial media have attracted great interest during the past 15 years and yielded ground-breaking electromagnetic and photonic phenomena. However, the high losses and strong dispersion associated with the resonant responses and the use of metallic structures, as well as the difficulty in fabricating the micro- and nanoscale 3D structures, have hindered practical applications of metamaterials. Planar metamaterials with subwavelength thickness, or metasurfaces, consisting of single-layer or few-layer stacks of planar structures, can be readily fabricated using lithography and nanoprinting methods, and the ultrathin thickness in the wave propagation direction can greatly suppress the undesirable losses. Metasurfaces enable a spatially varying optical response (e.g. scattering amplitude, phase, and polarization), mold optical wavefronts into shapes that can be designed at will, and facilitate the integration of functional materials to accomplish active control and greatly enhanced nonlinear response. This paper reviews recent progress in the physics of metasurfaces operating at wavelengths ranging from microwave to visible. We provide an overview of key metasurface concepts such as anomalous reflection and refraction, and introduce metasurfaces based on the Pancharatnam-Berry phase and Huygens' metasurfaces, as well as their use in wavefront shaping and beam forming applications, followed by a discussion of polarization conversion in few-layer metasurfaces and their related properties. An overview of dielectric metasurfaces reveals their ability to realize unique functionalities coupled with Mie resonances and their low ohmic losses. We also describe metasurfaces for wave guidance and radiation control, as well as active and nonlinear metasurfaces. Finally, we conclude by providing our opinions of opportunities and challenges in this rapidly developing research field.

Abstract: This Review covers the state-of-the-art technologies on photonics-based terahertz communications, which are compared with competing technologies based on electronics and free-space optical communications. Future prospects and challenges are also discussed. Almost 15 years have passed since the initial demonstrations of terahertz (THz) wireless communications were made using both pulsed and continuous waves. THz technologies are attracting great interest and are expected to meet the ever-increasing demand for high-capacity wireless communications. Here, we review the latest trends in THz communications research, focusing on how photonics technologies have played a key role in the development of first-age THz communication systems. We also provide a comparison with other competitive technologies, such as THz transceivers enabled by electronic devices as well as free-space lightwave communications.

Abstract: Metamaterials are composed of periodic subwavelength metal/dielectric structures that resonantly couple to the electric and/or magnetic components of the incident electromagnetic fields, exhibiting properties that are not found in nature. Planar metamaterials with subwavelength thickness, or metasurfaces, consisting of single-layer or few-layer stacks of planar structures, can be readily fabricated using lithography and nanoprinting methods, and the ultrathin thickness in the wave propagation direction can greatly suppress the undesirable losses. Metasurfaces enable a spatially varying optical response, mold optical wavefronts into shapes that can be designed at will, and facilitate the integration of functional materials to accomplish active control and greatly enhanced nonlinear response. This paper reviews recent progress in the physics of metasurfaces operating at wavelengths ranging from microwave to visible. We provide an overview of key metasurface concepts such as anomalous reflection and refraction, and introduce metasurfaces based on the Pancharatnam-Berry phase and Huygens' metasurfaces, as well as their use in wavefront shaping and beam forming applications, followed by a discussion of polarization conversion in few-layer metasurfaces and their related properties. An overview of dielectric metasurfaces reveals their ability to realize unique functionalities coupled with Mie resonances and their low ohmic losses. We also describe metasurfaces for wave guidance and radiation control, as well as active and nonlinear metasurfaces. Finally, we conclude by providing our opinions of opportunities and challenges in this rapidly developing research field.