Calculation Of Photoelectric Properties And Spectral Simulation Of Potassium-cesium-antimony Cathode

Potassium cesium antimony photocathode is widely used in photomultiplier tubes,because of its excellent photoemission performance in visible light band,it is also widely used in large area picosecond photodetectors and electron linear accelerators.Due to the uncontrollable factors in the process of preparing K₂Cs Sb photocathode at home and abroad,there will be some point defects such as vacancy defects and inversion defects in the preparation process.In addition,impurities in the antireflective coating materials will be doped in the K₂Cs Sb photocathode.In this paper,the first-principles calculation method based on density functional theory is used to study the point defects and impurity doping in the preparation process,and the spectral simulation study is carried out,this work will provide theoretical guidance for the structural design and preparation of K₂Cs Sb photocathode.Firstly,the electronic structures and optical properties of vacancy defects and inversion defects are calculated by first-principles method based on density functional theory.By comparing the formation energy of vacancy defects,it is found that the most easily formed vacancy defect type in the cathode preparation process is K₂Cs_0.75Sb.By comparing the formation energy and formation enthalpy of the inversion defects,it is found that the most easily formed and most stable reverse defect type is K₂Cs_0.75Sb_1.25.By comparing the conduction types of vacancy defect and inversion defects models,it is found that the point defect model with excess alkali metal has n-type semiconductor property,while the point defect model with excess Sb metal shows p-type semiconductor property.Secondly,the Ar+ion sputtering of X-ray photoelectron spectroscopy(XPS)was used to analyze the surface of K₂Cs Sb photocathode with antireflection film.It was found that Mg and Be elements impurities appeared in the K₂Cs Sb photocathode with Mg O and Be O antireflective films.Based on the first principles calculation,it is found that the formation energy of K₂Cs Sb doping model is positive except Be interstitial doping,which is not easy to form and unstable.In addition,interstitial doping and Cs inversion doping will reduce the absorption coefficient of K₂Cs Sb.First principles calculations of Mg and Be doped K₂Cs Sb(111)Cs surfaces show that the absorption coefficients of the other four surface doping models are higher than those of K₂Cs Sb(111)Cs surface model except for interstitial doping model.In addition,Mg and Be doping reduces the work function of K₂Cs Sb(111)Cs surface model,so electrons are easier to escape from the surface,which is more conducive to photoemission.Finally,based on the theory of thin film optical matrix,a simulation software for the design of transmission type K₂Cs Sb photocathode is designed.The influence of antireflection film,vacancy defect,inversion defects and doping in bulk model on the spectral properties of K₂Cs Sb photocathode was studied by this software.Under the condition of single antireflection film,Zr O₂ antireflection film has the best enhancement effect on the quantum efficiency and spectral response of transmission type K₂Cs Sb photocathode at 400 nm.Under the condition of double-layer antireflection film,Zr O₂-Ti O₂ antireflective film group has the best effect on improving quantum efficiency and spectral response.On the other hand,the single atom vacancy defects will reduce the quantum efficiency of the cathode.Among the inversion defects,the quantum efficiency of K_2.25Cs_0.75Sb are close to K₂Cs Sb,and the peak quantum efficiency of K₂Cs_0.75Sb_1.25 shifts to the long wave,while other inversion defects will reduce the quantum efficiency of the cathode.In addition,the substitution of K atoms will slightly improve the quantum efficiency,while the substitution of Cs atoms and interstitial doping will reduce the quantum efficiency.