In this letter, high power density AlGaN/GaN high electron-mobility transistors (HEMTs) on a freestanding GaN substrate are reported. An asymmetric Γ-shaped 500-nm gate with a field plate of 650 nm is introduced to improve microwave power performance. The breakdown voltage (BV) is increased to more than 200 V for the fabricated device with gate-to-source and gate-to-drain distances of 1.08 and 2.92 μm. A record continuous-wave power density of 11.2 W/mm@10 GHz is realized with a drain bias of 70 V. The maximum oscillation frequency (f_max) and unity current gain cut-off frequency (f_t) of the AlGaN/GaN HEMTs exceed 30 and 20 GHz, respectively. The results demonstrate the potential of AlGaN/GaN HEMTs on free-standing GaN substrates for microwave power applications.

This work demonstrates high-performance NiO/β-Ga₂O₃ vertical heterojunction diodes (HJDs) with double-layer junction termination extension (DL-JTE) consisting of two p-typed NiO layers with varied lengths. The bottom 60-nm p-NiO layer fully covers the β-Ga₂O₃ wafer, while the geometry of the upper 60-nm p-NiO layer is 10 μm larger than the square anode electrode. Compared with a single-layer JTE, the electric field concentration is inhibited by double-layer JTE structure effectively, resulting in the breakdown voltage being improved from 2020 to 2830 V. Moreover, double p-typed NiO layers allow more holes into the Ga₂O₃ drift layer to reduce drift resistance. The specific on-resistance is reduced from 1.93 to 1.34 mΩ·cm². The device with DL-JTE shows a power figure-of-merit (PFOM) of 5.98 GW/cm², which is 2.8 times larger than that of the conventional single-layer JTE structure. These results indicate that the double-layer JTE structure provides a viable way of fabricating high-performance Ga₂O₃ HJDs.

In this work, high-stability 4H-SiC avalanche photodiodes (APDs) for ultraviolet (UV) detection at high temperatures are fabricated and investigated. With the temperature increasing from room temperature to 150°C, a very small temperature coefficient of 7.4 mV/°C is achieved for the avalanche breakdown voltage of devices. For the first time, the stability of 4H-SiC APDs is verified based on an accelerated aging test with harsh stress conditions. Three different stress conditions are selected with the temperatures and reverse currents of 175°C/100 µA, 200°C/100 µA, and 200°C/500 µA, respectively. The results show that our 4H-SiC APD exhibits robust high-temperature performance and can even endure more than 120 hours at the harsh aging condition of 200°C/500 µA, which indicates that 4H-SiC APDs are very stable and reliable for applications at high temperatures.

基于最新研制的小阳极结反向并联肖特基二极管芯片，设计和制造了320~360 GHz固定调谐分谐波混频器。混频器的结构采用的是传统电场（E）面腔体剖分式结构：将二极管芯片倒装焊粘在石英基片上，再用导电银胶将石英电路悬置粘结在混频器下半个腔体上。电路设计采用场路相结合的方法：用场仿真软件建立混频电路各个功能单元的S参数模型，将它们代入非线性电路仿真软件中与二极管结相结合进行混频器性能整体仿真优化。最终测试结果表明，谐波混频器的双边带在4~6 mW的本振功率驱动下，在320~360 GHz超过12%带宽范围内，双边带变频损耗均小于9 dB；混频器在310~340 GHz频带范围内，双边带噪声温度最低为780 K。声温度最低为780 K。

2D material of graphene has inspired huge interest in fabricating of solid state gas sensors. In this work, epitaxial graphene, quasi-free-standing graphene, and CVD epitaxial graphene samples on SiC substrates are used to fabricate gas sensors. Defects are introduced into graphene using SF₆ plasma treatment to improve the performance of the gas sensors. The epitaxial graphene shows high sensitivity to NO₂ with response of 105.1% to 4 ppm NO₂ and detection limit of 1 ppb. The higher sensitivity of epitaxial graphene compared to quasi-free-standing graphene, and CVD epitaxial graphene was found to be related to the different doping types of the samples.

In this work, we investigate the influence of defect concentration of the diamond substrates on the performance of hydrogen-terminated diamond field-effect transistors by Raman spectra, pulsed I–V characteristics analysis, and radio frequency performances measurements. It is found that a sample with higher defect concentration shows larger drain-lag effect and lower large-signal output power density. Defects in the diamond act as traps in the carrier transport and have a considerable influence on the large-signal output power density of diamond field-effect transistors. This work should be helpful for further performance improvement of the microwave power diamond devices.