基于叠层复合结构的GaAs基光电阴极宽光谱响应增强研究

Because of the shortwave threshold in window layer of traditional transmission-mode GaAs-based photocathode, it is difficult to achieve the broadband spectral response from ultraviolet to near-infrared. To explore a photocathode with spectral response covering the whole band from ultraviolet to near-infrared, we will investigate the enhancement of broadband spectral response for reflection-mode GaAs-based photocathode with the laminated composite structure in this project. Firstly, a laminated composite structure of reflection-mode GaAs-based photocathode with distributed Bragg reflector superlattice and graded-composition and graded-doping structure will be designed, through overall consideration of optical absorption, band structure and lattice matching. According to this structure, the photoemission model of reflection-mode GaAs-based photocathode with characteristics of the enhanced optical absorption and the assisted electric field will be established. Then, the epitaxial growth and activation experiment will be implemented, and the process of photocathode preparation will be optimized. Lastly, the reflection-mode GaAs-based photocathode with broadband spectral response from ultraviolet to near-infrared will be developed by improving the quantum efficiency and surface stability. Moreover, the research on the prototype of reflection-mode vacuum optoelectronic device will be carried out. This project is an exploration of reflection-mode vacuum optoelectronic devices with high sensitivity and broadband spectral response. The reflection-mode GaAs-based photocathodes with the laminated composite structure have great potential for applications in the fields of low-light-level night vision, solar cells, high-energy physics, astronomical observation and environmental monitoring etc.

传统的透射式GaAs基光电阴极由于窗口层存在短波阈值，难以实现紫外至近红外全波段响应特征，为了探索一种能够覆盖从紫外至近红外全波段响应的光电阴极，本项目根据光电阴极反射式工作模式特点，拟开展基于叠层复合结构的GaAs基光电阴极宽光谱响应增强研究，从光学吸收、能带结构、材料晶格匹配方面考虑，设计一种具有分布式布拉格反射超晶格结构、变组分变掺杂结构的反射式GaAs基光电阴极复合结构，建立综合光吸收增强和电场辅助特点的反射式GaAs基阴极光电发射模型，开展阴极材料外延生长和激活实验，优化制备工艺，从提高量子效率和增强稳定性两方面着手，研制出实现紫外至近红外宽光谱响应的反射式GaAs基光电阴极，并开展反射式原型真空光电器件研究。本项目是对高灵敏度、宽光谱响应反射式真空光电器件的一种探索。反射式叠层复合GaAs基光电阴极在微光夜视、太阳电池、高能物理、天文观测、环境监测等领域将具有广泛的应用前景。

为了突破传统透射式GaAs基光电阴极短波阈值的限制，探索一种能够覆盖从紫外至近红外全波段响应的光电阴极，本项目开展了叠层宽光谱响应GaAs基光电阴极的光电发射模型、结构设计、材料生长、质量表征、表面激活和器件试验研究。从光学吸收、能带结构、材料晶格匹配方面考虑，设计了能够提高近红外光响应的GaAs基光电阴极复合结构，结合了变组分变掺杂结构和分布式布拉格反射结构，建立了具有光吸收增强和电场辅助作用的光电发射理论模型，包括稳态下的量子效率模型和非稳态下的时间响应模型；利用MOCVD在GaAs衬底上外延生长了在1064nm处具有极小反射率的叠层复合GaAs基光电阴极材料，对表面反射率和粗糙度、各子层厚度和元素深度分布进行了测试验证；结合第一性原理计算，从理论上揭示了能够提升GaAs基光电阴极量子效率和寿命的Cs/NF3激活机理，实验上探索出了利用近红外激光补Cs/O激活提高阴极近红外响应的激活方法，以及进一步提高阴极稳定性的Cs/O/NF3激活方法；基于新建的光电阴极制备与表征超高真空互联系统，开展了GaAs基光电阴极基于不同工艺的表面净化过程、激活过程和衰减过程的原位性能表征，优化了阴极制备工艺；研制了具有反射式和透射式双工作模式的宽光谱响应GaAs基光电阴极原型真空光电器件，验证了增大施加偏压对反射式和透射式光谱响应具有显著提高作用。与传统结构GaAs基光电阴极相比，叠层复合GaAs基光电阴极在1064nm波长处的反射率降低了75%，量子效率提高了9倍；与Cs/O激活方法相比，Cs/NF3激活方法能够提升1064nm波长处的量子效率3倍以上。本项目研究成果为研制高灵敏度、高稳定性的宽光谱响应真空光电器件奠定了良好基础，提出的新激活方法有望在我国三代微光像增强器的生产中获得应用，基于叠层复合GaAs基光电阴极能够研制1064nm波长响应增强的近红外光电倍增管，应用于激光测距、激光雷达、光子计数、荧光光谱等民用领域。