Study Of GaAs Photocathode With High Performance

Negative electron affinity gallium arsenide (GaAs) photocathode has many virtues, such as high quantum efficiency, low dark current, concentrated electrons energy distribution and angle distribution, adjustive long-wave threshold, great potential to extend the long-wave spectral response waveband and so on. The third generation low-light-level (LLL) imaging intensifier, in which GaAs photocathode acts as a core component, has extended the long-wave threshold and visual distance of night vision instruments, and therefore it is widely applicated in LLL night vision.After several generations researchers' efforts a comparative complete manufacture line of the third generation imaging intensifier has been established in our nation, but national prepared GaAs photocathodes have big distance from foreign ones in sensitivity and stability. To expedite national research course on GaAs photocathodes, and make it achieve application level and rapidly equipped for army, the study of GaAs photocathode theory, material structure, activation technique and performance measurement and evaluation was made in this dissertation. The research work encircles the intention to achieve GaAs photocathode with high performance, and it is supported by the tenth five-year national defence emphasized demonstration and validation project on measurement technology of X X X, and also by the tenth five-year national defence emphasized pre-research project on night vision technology of X X X. The content in this dissertation is summarized as follows:In the first chapter the development history of GaAs photocathode is reviewed. The contents on GaAs photocathode to research and explore are pointed out on the basis of the analysis of the research status in quois and performance distance between national and foreign GaAs photocathode. The intention and signification of this dissertation are expatiated, and the main research work in this dissertation is introduced.In the second chapter the theory of spectral response of GaAs photocathode is studied in detail. Firstly, the photoemission mechanisms of GaAs photocathode are introduced, and the deduction of quantum efficiency formulas of GaAs photocathode under different operation modes is made. Then, the quantum efficiency formulas which include front surface recombination velocity are firstly deduced for reflection-mode and transmission-mode GaAs photocathodes by use of integral deduction method. Theinfluences of performance parameters on the quantum efficiency and integral sensitivity of GaAs photocathode are analyzed, and the methods to calculate performance parameters are introduced.In the third chapter the development of multi-information measurement and evaluation system of GaAs photocathode is introduced. Firstly the system whole structure is introduced, and then the structure and performance of super high vacuum activation system, the construction of multi-information on-line monitoring system and work principle of surface analysis system are introduced respectively, thereinto the development of engineering machine of spectral response measurement instrument are introduced in detail.In the fourth chapter the activation technique and its optimizations of GaAs photocathode are studied. Firstly, the influences of first deposition amounts of Cs, the ratio of Cs to O and the different ativation manners on the characteristic of spectral response and stability of photocathode are compared and analyzed. Then, the inherent mechanisms of high-low temperature two step activation technique are explored by use of the surface analysis technology of angle-dependent X-ray photoelectron energy spectrum (XPS). Finally, the optimized approaches of activation technique for GaAs photocathode are established.In the fifth chapter the material structure of varied doping GaAs photocathode in which from bulk and surface the doping concentrations are distributed from high to low is firstly put forward, and the experimental and theoretic research on it is made in detail. Firstly, the design and molecular beam epitaxy (MBE) preparation of three kinds of reflection-mode varied doping GaAs photocathode materials are made, and the contradistinctive activation experiments, the measurement of spectral response and stability of varied doping GaAs photocathode materials and uniform doping GaAs photocathode materials are made, which has validated the feasibility that varied doping GaAs photcathode can achieve higher quantum efficiency in experiment. Then, the photoemission mechanisms of varied doping GaAs photocathode are discussed according to its energy band structure, and the quantum efficiency formulas of varied doping GaAs photocathode are deduced. Finally, the farther approaches to optimize the varied doping GaAs photocathode structure are established.In the sixth chapter the uniformity, stability under illuminations with different intensity, and spectral response before and after indium-sealed of GaAs photocathode in the third generation experimental tubes are firstly explored by use of engineering...