The GaN HEMT is a potential candidate for RF applications due to the high frequency and large power handling capability. To ensure the quality of the communication signal, linearity is a key parameter during the system design. However, the GaN HEMT usually suffers from the nonlinearity problems induced by the nonlinear parasitic capacitance, transconductance, channel transconductance etc. Among them, the transconductance reduction is the main contributor for the nonlinearity and is mostly attributed to the scattering effect, the increasing resistance of access region, the self-heating effect and the trapping effects. Based on the mechanisms, device-level improvement methods of transconductance including the trapping suppression, the nanowire channel, the graded channel, the double channel, the transconductance compensation and the new material structures have been proposed recently. The features of each method are reviewed and compared to provide an overview perspective on the linearity of the GaN HEMT at the device level.

Space Debris Laser Ranging (DLR) is a technique to measure range to defunct satellites, rocket bodies or other space targets in orbits around Earth. The analysis shows that one of the reasons for the low success probability of DLR is the inaccurate orbital prediction of targets. Then it is proposed to use the Superconducting Nanowire Single-Photon Detector (SNSPD) running in automatic-recoverable range-gate-free mode, in which case, the effect of the accuracy of the target’s orbital prediction on the success probability of DLR is greatly reduced. In this way, 249 space debris were successfully detected and 532 passes of data were obtained. The smallest target detected was the space-debris (902) with an orbital altitude of about 1000 km and a Radar Cross Section (RCS) of 0.0446 m². The farthest target detected was the space-debris (12,445) with a large elliptical orbit and an RCS of 18.2505 m², of which the range of the normal point (NPT) of the measured arc-segment on January 27, 2019 was 6260.805 km.

Disposable devices designed for single and/or multiple reliable measurements over a short duration have attracted considerable interest recently. However, these devices often use non-recyclable and non-biodegradable materials and wasteful fabrication methods. Herein, we present ZnO nanowires (NWs) based degradable high-performance UV photodetectors (PDs) on flexible chitosan substrate. Systematic investigations reveal the presented device exhibits excellent photo response, including high responsivity (55 A/W), superior specific detectivity (4x10¹⁴ jones), and the highest gain (8.5x10¹⁰) among the reported state of the art biodegradable PDs. Further, the presented PDs display excellent mechanical flexibility under wide range of bending conditions and thermal stability in the measured temperature range (5–50 °C). The biodegradability studies performed on the device, in both deionized (DI) water (pH≈6) and PBS solution (pH=7.4), show fast degradability in DI water (20 mins) as compared to PBS (48 h). These results show the potential the presented approach holds for green and cost-effective fabrication of wearable, and disposable sensing systems with reduced adverse environmental impact.

Photonic integrated circuits (PICs) are expected to play a significant role in the ongoing second quantum revolution, thanks to their stability and scalability. Still, major upgrades are needed for available PIC platforms to meet the demanding requirements of quantum devices. We present a review of our recent progress in upgrading an unconventional silicon photonics platform toward this goal, including ultralow propagation losses, low-fiber coupling losses, integration of superconducting elements, Faraday rotators, fast and efficient detectors, and phase modulators with low-loss and/or low-energy consumption. We show the relevance of our developments and our vision in the main applications of quantum key distribution, to achieve significantly higher key rates and large-scale deployment; and cryogenic quantum computers, to replace electrical connections to the cryostat with optical fibers.