基于AlGaN光电阴极的太赫兹真空器件电子源发射机理及制备技术研究

In view of the electron source with high temperature and low current density of THz electronic devices, this project provides the AlGaN photocathode based electron source with frequency laser. The AlGaN photocathode is designed with varying composition structure and graded doping surface, which can improve the movement of the photoelectron excitated at the interior emission-layer toward photocathode surface and escape to the vacuum eventually. By using the first-principles, the energy band structure and the surface state of the AlGaN photocathode is calculated, and the effecting of depletion layer width and built-in field size on the electron movement are also studied. The electron emission module of photocathode with varying composition and graded doping structure could be built. The optimal optical structure of the emission-layer will be design. The preparation technology for induce the electron affinity and evaluate photoemission performance of the photocathode could be studied, and testing the performance of photocathode with frequency laser. Compare with the result of the experiment and theory calculation, it is shortcut to optimal the photocathode structure and preparation technology, in which way the electron density of photocathode could be up to 2 A/cm2. This is an exploration for electron source with high frequency vacuum device, and plans to resolve the traditional cathode performance with high temperature and low reliable. The photocathode electron source with lease modulation could help the development of the THz vacuum device.

针对太赫兹真空器件对低温和大电流密度电子源性能的要求，本项目提出飞秒激光脉冲响应的AlGaN光电阴极电子源。AlGaN光电阴极采用变组分结构和变掺杂表面的设计方法，促使内部激发的光电子向阴极表面定向输运最终逸出阴极表面形成电子发射。通过第一性原理计算AlGaN光电阴极能带结构和表面态以及界面处耗尽层的宽度、内建电场对电子扩散运动的影响，建立变组分变掺杂光电阴极电子发射模型，设计最佳阴极发射层光学结构，研究降低阴极电子亲和势的制备方法与阴极电子发射性能评估方法，制备基于AlGaN光电阴极的真空光电二极管，测试AlGaN光电阴极对飞秒激光脉冲的响应特性，最终使光电阴极的脉冲电流密度达到2 A/cm2。本项目是对新型高频率真空器件电子源的一种探索，拟解决传统阴极工作温度高和可靠性低等问题，飞秒激光脉冲调制光电阴极电子源可进一步推动太赫兹真空器件发展。

为了满足真空微波器件对高性能电子源的需求，开展了快响应、大电流密度、免激活光电阴极电子发射理论和制备工艺研究。获得了低功函数阴极材料结构模型、真空沟道结构光电阴极设计方法及其制备工艺；测试了不同条件下光电阴极电子发射特性；光电阴极直流发射电流密度达到5.33A/cm2，脉冲发射电流密度达到2.3 A/cm2，达到了670GHz和850GHz真空微波器件对阴极发射电流的要求。主要研究内容包括光电阴极表面原子结构仿真、光电阴极组件结构设计、光电阴极组件性能仿真、光电阴极组件材料特性、光电阴极组件制备工艺和阴极组件电子发射特性测试与性能评估。本项目研制的光电阴极可有效提高行波管器件的启动速度和可靠性。