| Negative electron affinity gallium arsenide (GaAs) photocathodes have been developed for more than 40 years, and have achieved remarkable successes in the cathode theory, preparation techniques, surface models and characterization techniques. Accordingly, GaAs photocathodes are widely applied in the low-light-level (LLL) imaging intensifier and vacuum electron sources. However, the photoemission theory of GaAs cathodes is not very perfect, and only a few measurement and characterization techniques are used for cathode preparation, these restrict the further development of GaAs cathodes. At the same time, in order to meet the demands of new application domain of GaAs photocathodes, the higher quantum efficiency and stability are required for them. In order to overcome these obstacles or meet the demands faced by GaAs photocathode, we performed some thorough studies in the electron transport and quantum efficiency theory, characterization techniques, cathode preparation techniques and mechanism, cathode stability, and varied-doping GaAs cathode theory and experiments.Based on Spicer's "Three-step Model" about photoemission, we studied the photoemission theory of GaAs photocathode thoroughly. We solved the equation of electron escape probability from the Schrodinger equation, and calculated the emitted electron energy distribution of GaAs photocathodes. We presented a new quantum efficiency equation for reflection-mode photocathode, in which many factors was considered. According to the fitting of the quantum efficiency crves based on the new equation, the cathode surface potential barrier and cathode performance can be characterized.We designed and improved the measurement and characterization system for GaAs photocathode, in which we developed the multi-information measurement and control system. The system can measure the photocurrent, spectral response, currents of Cs and O sources, and vacuum pressure on-line. Based on these measured experimental data, we improved the supervised technologies for cathode preparation, and developed the situ characterization techniques for cathode performance.The preparation techniques of GaAs photocathodes and its mechanism were studied. Using the X-ray photoelectron energy spectrum (XPS), we analyzed the effect of chemical cleaning and heat cleaning on the single crystal wafer and MBE epitaxial wafer. Based on the pressure variation during the heat cleaning, we developed a simple and on-line characterization technique about the effect of heat cleaning on cathode surface. The effect of Cs/O flux ratios on cathode activation and the mechanism of it were studied, and the variation rule of photocurrent was revealed.The effects of illumination intensity, photocurrent and Cs pressure on cathode stability were studied. Based on the adsorption of harmful gases on the cathode surface, an equation about the relationship between the cathode lifetime and the pressure was deduced theoretically. We found the variation of quantum efficiency curves during the degradation process of cathode, and investigated the relationship between the variation of curves and the profile of cathode surface potential barrier. According to the angle-dependent XPS analysis, we charaterized the evolution of potential barrier and revealed the mechanism of cathode stability.In order to achieve higher quantum efficiency cathode, we carried out the theoretical and experimental studies on varied-doping GaAs photocathodes. Based on the band structure model, we solved the quantum efficiency equations and resolution equations of exponential-doping cathodes from the minority continuity equations, and using these equations calculated the theoretical quantum efficiency and resolution of exponential-doping cathodes. Finally, we designed and prepared some varied-doping GaAs photocathodes. The integral sensitivities of prepared gradient-doping cathode and exponential-doping cathode are 1798μA/lm and 1956μA/lm, respectively, which is about 30% higher than that of uniform-doping cathodes.
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