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。

提出了一种基于片上集成电容工艺和带阻滤波结构的高功率三倍频器设计方法。在倍频器输入端，首先对倍频器二极管的直流偏置馈电部分进行改进，在梁式引线结构基础上结合二氧化硅（S_iO₂）工艺实现了片上集成电容，同时解决了三倍频器的直流馈电和射频接地问题，实现电路功能集成的同时也提高了模型仿真精度。此外，在二极管的输入端采用带阻滤波器结构替代传统的低通滤波结构，在保证倍频器性能的同时进一步简化倍频器结构复杂度和尺寸。为进行验证，设计并加工测试了两款中心频率分别为110 GHz和220 GHz的双路功率合成三倍频器。实际测试结果表明，在输入功率500 mW条件下，110 GHz三倍频器的输出峰值功率达到了140 mW，峰值效率接近30%，带宽超过15 GHz；在输入功率300 mW条件下，220 GHz三倍频器的输出峰值功率达到了45 mW，峰值效率达到15%，带宽为15 GHz。两款倍频的测试结果均有优秀表现，验证了设计方法的有效性。

Ultraviolet (UV) detectors with large photosensitive areas are more advantageous in low-level UV detection applications. In this Letter, high-performance 4H-SiC p-i-n avalanche photodiodes (APDs) with large active area (800 μm diameter) are reported. With the optimized epitaxial structure and device fabrication process, a high multiplication gain of 1.4 × 10⁶ is obtained for the devices at room temperature, and the dark current is as low as ～10 pA at low reverse voltages. In addition, record external quantum efficiency of 85.5% at 274 nm is achieved, which is the highest value for the reported SiC APDs. Furthermore, the rejection ratio of UV to visible light reaches about 10⁴. The excellent performance of our devices indicates a tremendous improvement for large-area SiC APD-based UV detectors. Finally, the UV imaging performance of our fabricated 4H-SiC p-i-n APDs is also demonstrated for system-level applications.

In this Letter, we report large-area (600 μm diameter) 4H-SiC avalanche photodiodes (APDs) with high gain and low dark current for visible-blind ultraviolet detection. Based on the separate absorption and multiplication structure, 4H-SiC APDs passivated with SiNx instead of SiO2 are demonstrated for the first time, to the best of our knowledge. Benefitting from the SiNx passivation, the surface leakage current is effectively suppressed. At room temperature, high multiplication gain of 6.5×105 and low dark current density of 0.88 μA/cm2 at the gain of 1000 are achieved for our devices, which are comparable to the previously reported small-area SiC APDs.