Abstract：AlAs/InGaAs/AlAs resonant tunneling materials was optimized, and terahertz resonant tunneling diodes grown by MOCVD is first fabricated. The epitaxial layers of the RTD were grown on semi-insulating InP substrate. InP-based RTD were fabricated by using contact lithography and air bridge technology.The electrical characteristics of the device were tested at room temperature. The peak current density of our RTD exceeded 400 kA/cm2, and the peak to valley current ratio of our RTD was 2.4.

Abstract：The terahertz(THz) wave is located in the transition region of photonics to electronics, and has important application prospects in high-speed broadband communication, radar, imaging and other fields. However, the devices currently used for dynamic regulation of THz waves are still lacking, which limits the development of THz technology to some extent. VO2 has an unique metal-insulator phase change characteristic, and the phase change process can be applied to dynamically regulate THz wave transmission. It is also a recent research hotspot to explore the combination of metamaterials and VO2 to prepare efficient, dynamic and flexible terahertz functional devices. In this paper, the phase transition characteristics of VO2 are briefly described, and the effects of microstructure and chemical composition on phase transition characteristics are analyzed. The research progress of VO2 film in THz band regulation performance is reviewed systematically, and the different combinations of VO2 and metamaterials are summarized. In the application of THz wave dynamic regulation, the development prospects and challenges of THz wave regulation function devices based on VO2 phase transition characteristics are prospected.

Abstract：With the development of semiconductor technology, characteristic frequency of transistors have been improving so far and into THz frequency range, which makes it possible for solid state devices to work in THz frequency range. THz amplifier plays a key role in THz system because of its function amplifying weak THz signals. This paper introduces the latest research progress of THz monolithic amplifier based on Gallium Nitride(GaN) High Electron Mobility Transistor(HEMT)，Indium Phosphide(InP) HEMT and InP Heterojunction Bipolar Transistor/Double Heterojunction Bipolar Transistor(HBT/DHBT).

Abstract：At present, optically controlled terahertz band metamaterials are mainly realized by changing the carrier concentration of semiconductor materials with laser. The composite lifetime of semiconductor materials is generally in nanosecond order, which limits the controlling time. Compared with semiconductor materials, CS2 has a fast light response time of about 1.68 ps and large optical nonlinearity. Based on the structure of sub-wavelength periodic metal block arrays, a strategy to adjust terahertz transmission of metamaterials using CS2 is proposed. Specifically, the control of terahertz wave transmission in this structure is studied by finite difference time domain(FDTD).

Abstract：In this paper, the current development status and bottleneck problems of terahertz science and technology are presented. The emphasis of discussion is on research progress of the core component in terahertz circuits, monolithic integrated power amplifier. According to the kinds of base material in integrated circuit(IC) design, compound including InP and GaAs terahertz amplifier IC are compared with those made by silicon including bulk CMOS and SiGe. Basing on this category standard by material, the performances of terahertz amplifier IC are analyzed and concluded in the aspects of circuit topology and specifications.

Abstract：The structure and dimension of Schottky diode were designed. The loss at high frequency was reduced using a quasi-whisker contacted anode structure by a metal finger akin to an air bridge. The nonlinear model of Schottky anode and three dimensional electromagnetic(EM) model were established respectively according to the measured data and structure of Schottky diode. The diodes were placed in waveguide using balanced circuit design. The EM mode orthogonality ensured very good input and output signal isolation, which simplified the circuit structure and reduced the circuit loss. A 300 GHz doubler was designed and fabricated successfully. The efficiency is higher than 5% at 312～319 GHz with a peak efficiency of 10.1% at 316 GHz. The output power is higher than 4 mW at 307～318 GHz with a peak output power of 8.7 mW at 316 GHz. The diodes are replaced by one with higher doping concentration. The peak efficiency is 13.7% and the peak output power is 11.8 mW which reaches the similar level of reported doublers. The results proved the ability of Schottky diode working at high frequency.

Abstract：Metasurface, a novel artificial electromagnetic material, its thickness is much smaller than the wavelength. By regulating the interaction between the sub-wavelength unit structure and the electromagnetic wave, the wave will undergo a phase or amplitude mutation after passing through the metasurface, so as to realize the regulation of the propagation direction, waveform and polarization mode of the electromagnetic wave. Compared with 3D metamaterials, the metasurface not only inherits the original ability of the electromagnetic wave manipulation, but also has the advantages of low loss, thin thickness and easy integration, thus attracting the attention of researchers all over the world. Terahertz metasurface devices show great potential in planar meta-lenses, vortex beams, digital coded metasurface and holographic imaging, etc. In this review, the phase control principle of the metasurface is analyzed, the characteristics and applications of several kinds of important metasurface devices are summarized, and the challenges in the future and the direction of further development of the metasurface are prospected.

Abstract：Science and technologies based on terahertz radiation have developed rapidly over the recent decades, which inspires the application attempts and research of terahertz technologies in several fields. Compared with the microwave or infrared waves, terahertz waves are of higher frequencies and lower photon energy. A variety of dielectrics are transparent with the terahertz radiation. Status and progresses in the field of terahertz communication, biological and medical application, non-destructive testing, and defense and security imaging are discussed in this work, as well as the challenges for real-life applications.