Negative Electron Affinity GaAs Photocathode Cs/NF₃ Activation Technology And Characteristic Evaluation

Due to the advantages of concentrated electron emission angle,high spin polarizability,and high quantum efficiency,GaAs photocathode is applied in low-level-light night vision and high-energy physics.The stability of GaAs photocathode is an important parameter to describe its performance and the stability can be improved by a suitable activation process.Therefore,in order to improve the activation process of the GaAs photocathode,enhance the stability of GaAs photocathode and make GaAs photocathode be used in more fields,this article has executed a research on the adsorption model,NF₃ gas flow control,Cs/NF₃activation method and photocathode stability.Firstly,different absorption models of GaAs surface were constructed using the first-principles calculation based on density functional theory.Variations in material properties during Cs/NF₃ adsorption process were analyzed,by comparing the adsorption models of different Cs/NF₃ ratios,the calculation results show that absorption model of 6Cs/1NF₃ ratio owns the least work function and relatively larger absorption energy.Compared with the Cs/O model at the same adsorption ratio,the results show that GaAs surface model of Cs/NF₃adsorption is a more stable model.It provides theoretical guidance for the further study of Cs/NF₃ activation process.Secondly,the improved photocathode preparation and characterization ultra-high vacuum interconnection system was introduced,and the components of this system were described.The system can realize multi-information on-line measurement and control,including information such as the activation photocurrent,the vacuum degree of the system,and the current of the activation source.The process of obtaining ultra-high vacuum by the the system was introduced,and a method of micro-adjustable inlet of high-purified NF₃ gas was proposed.Nextly,Cs/NF₃ activation experiment with high temperature and low temperature of GaAs photocathode were designed.We analyzed the effect of two-step activation process with high temperature and low temperature.The results show that two-step activation process with high temperature and low temperature can increase the quantum efficiency of GaAs photocathode in the Cs/NF₃activation process.Finally,We conducted a stability test of GaAs photocathode after Cs/NF₃ activation experiment.We tested the photocurrent decay of GaAs photocathode after activation under light conditions and the decay of quantum efficiency of GaAs photocathode without light.Cs/O activation experiment was designed for the comparison,experimental results show that the stability of GaAs photocathode activated by Cs/NF₃ activation is better than Cs/O activation.