变掺杂NEA GaN光电阴极材料特性与量子效率理论研究

For variable doping GaN photocathode, the quantum efficiency can be increased by adopting the variable doping method. That is to say, in the photoemission layer, the bulk doping concentration is high, and doping concentration is decreased gradually from bulk to surface, thus the built-in field is built. By the means of combining experiment and theory, the research of material characteristics and quantum efficiency theory for variable doping NEA GaN photocathode material will be carried out. By the electron transportation characteristic from bulk to surface of variable doping GaN photocathode, the energy band structure and the built-in field for variable doping GaN photocathode will be studied. The quantum efficiency theory of variable doping NEA GaN photocathode will be probed into. And the best structure of variable doping GaN photocathode will be designed with the quantum efficiency theory. By the means of testing the surface photovoltage spectroscopy etc., the performance evaluation means can be completed, the photovoltaic characteristics and the surface layer structure will be studied. The preparation experiments for variable doping GaN photocathode will be carried out. And the comparative analysis will be completed with the theory results. By optimizing the material design continuously, the quantum efficiency of GaN photocathode will be more than 50%.This project has important theory significance and application value to develop the theory research on variable doping GaN photocathode and promote the development of UV detection, high energy physics, microelectronics and electron beam lithography etc..

变掺杂GaN光电阴极是指在光电发射层内，通过采用体内掺杂浓度高，往表面浓度逐渐降低的变掺杂方法，构建从内到外的内建电场，提高阴极量子效率。本项目将运用实验和理论相结合的方法，开展变掺杂NEA GaN光电阴极材料特性与量子效率理论研究。本项目通过电子从变掺杂NEA GaN光电阴极体内到表面的输运特性，研究变掺杂阴极材料的能带结构和内建电场；探索变掺杂NEA GaN光电阴极量子效率理论；利用量子效率理论设计最佳变掺杂GaN光电阴极结构；通过测试材料表面光电压谱等方法，完善变掺杂材料性能表征手段，研究阴极材料表面光伏特性和表面层结构；进行变掺杂阴极材料的制备实验，并和理论结果进行对比分析，通过不断优化材料设计，使制备的阴极量子效率达到50%以上。本课题对开展高性能变掺杂GaN光电阴极研究，推动我国紫外探测、高能物理、微电子学和电子束平版印刷技术等领域的发展，具有重要的理论意义和应用价值。

本课题运用实验和理论相结合的方法，开展了高性能变掺杂NEA GaN光电阴极材料特性与量子效率理论研究。从变掺杂负电子亲和势（NEA）GaN光电阴极材料的光电发射机理和能带模型入手，给出了变掺杂NEA GaN光电阴极内建电场和量子效率的计算公式。根据变掺杂紫外光电阴极的特点改进了光电阴极制备及测控系统。结合设计的变掺杂GaN阴极掺杂结构，研究了GaN光电阴极材料的表面反射率、光学折射率、光谱吸收系数以及透射光谱等光学参数。给出了均匀掺杂GaN光电阴极的光谱吸收系数的特点，根据变掺杂NEA GaN光电阴极的结构特点，给出了光谱平均吸收系数的概念和等价计算公式，并对均匀掺杂与变掺杂NEA GaN光电阴极光谱吸收系数进行了对比。研究了GaN光电阴极材料的电子扩散长度、电子迁移率、电导率等电学特性参数，推导了变掺杂GaN阴极材料的电子扩散漂移长度的计算公式。进行了变掺杂 GaN光电阴极的净化、激活和量子效率在线测试与评估实验。在此基础上，建立了变掺杂GaN光电阴极发射表面模型。根据半导体光电发射理论和双偶极层模型，通过对电子亲和势随铯覆盖度变化的实验结果进行拟合运算，得到了电子亲和势与铯覆盖度之间的函数关系式。研究了变掺杂NEA GaN光电阴极激活时铯的吸附机理。制备的变掺杂NEA GaN光电阴极在240 nm处得到了56％的量子效率，在较宽的入射光波长范围内，阴极具有相对平稳的量子效率，量子效率值随入射光子能量的增加而增加，并且量子效率曲线在阈值附近表现出了明显的锐截止特性。项目研究达到了预期目标。在目前材料性能的局限下，项目研究成果为进一步提高GaN光电阴极的量子效率从根本上找到了解决办法，对进一步开展高性能紫外光电阴极研究具有很好的借鉴作用。