超导纳米线光学特性及其机制研究

Superconducting nanowire is the core component of superconductor single photon detectors (SSPD). Its optical property is one of the key factors that affect the device efficiency. The present study the electrical properties of superconducting nanowires more in-depth, but few studies of its optical properties. The project intends to study the optical reflection, transmission and absorption with temperature, bias current and magnetic field on superconducting nanowires. On the basis of the existing processes and systems, superconducting nanowires of different geometries will be fabricated after further optimization of materials and device technology. The influence of temperature, current and magnetic field on the above optical properties will be investigated in experiment. Also, the relation of hot spots and flux to current and magnetic field will be studied. Then, the optical properties can reveal many micro-phenomena, such as hot spots and flux. Those enable us to explore the microscopic mechanisms between photons and superconductor. Through these studies, it is possible to facilitate the understanding of SSPD photon response mechanism to promote research and development of new SSPD devices and revealing the physical laws of superconductor-photon interaction.

超导纳米线是超导单光子探测器(SSPD)核心组成部分，其光学特性是影响器件光子响应和检测效率的关键因素之一。但目前其光学特性研究较少,特别是在电流偏置等条件下的光学特性尚无报道。 本项目拟研究不同温度、偏置电流和外加磁场作用下超导纳米线的反射、透射和吸收等光学特性。基于这些光学特性，结合低温超导理论,探索超导纳米线中库伯对、非平衡载流子、热点和磁通等对光学特性的影响，进而揭示超导体与光子相互作用的微观机制。通过上述研究，有望获得光子与超导体相互作用的物理规律，促进对SSPD光子响应机制的认识，推动新型SSPD器件研发。

超导纳米线是超导单光子探测器(SSPD)器件核心组成部分，其光学特性是影响器件光子响应和性能的关键因素之一。目前超导纳米线电学特性研究比较深入，但其光学特性研究较少。本项目在已有工艺和系统的基础上，进一步优化材料和器件工艺，研制不同几何结构的超导纳米线。结合实验数据和仿真结果, 系统研究了多种氮化铌超导纳米线探测器器件结构的光学特性。在背面对光结构中，采用双面SiN的硅衬底结构的背面器件，其NbN的吸收效率比双面热氧化的硅衬底结构要高很多，可达99.3%，但与正面对光结构相比，带宽都较小，不适用于宽谱响应。正面对光结构中，与Au镜为反射镜的正面器件相比，以DBR镜为反射镜的正面器件在牺牲部分带宽宽度的情况下可以获得更高的吸收效果，吸收率高达99.9%。NbN薄膜厚度从5nm开始逐渐增加时，各器件的吸收率均会随之降低。这些结果为高效率器件的设计和研究提供了重要依据。

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