Study On Theoretical Model And Preparation Technology Of GaAs-base Electron-injection Cathode

Gallium arsenide(GaAs)photocathode has been widely used in electron accelerators and low-light-level night vision due to its advantages of high polarizability,low energy dispersion and high brightness.With the development of these fields,the quality requirements of the electron beam are also increasing,and a longer operating lifetime of the cathode is needed while obtaining high polarizability and high brightness electron beam.GaAs-based electron-injection cathode has the same advantages as GaAs photocathode,and because it does not require expensive and complex laser drive system to illuminate the cathode surface,the operating lifetime of the cathode is effectively extended.As a new type of cathode,the electron-injection cathode uses electric drive to achieve electron emission,therefore the emission current density and electron beam pulse structure can be flexibly controlled by the electrical signal,which is expected to satisfy the current cathode performance requirements and further promote the development of vacuum electronic devices.In this paper,the working mechanism of electron-injection cathode was described in detail,and the theoretical model of electron-injection cathode was established.The optimal range of Al GaAs/GaAs epitaxial layer parameters and emission array parameters was obtained by simulating the performance of electron-injection cathode with the theoretical model.On the basis of simulation,the preparation technology of electron-injection cathode and its relative performance were studied.The simulation results showed that the linear decreasing distribution of Al composition in the graded bandgap p-Al GaAs layer can form a built-in electric field and improve the emission current efficiency of electron-injection cathode.The Al composition in the p-Al GaAs layer was less than that in the n-Al GaAs layer,which can inhibit the hole current,and the emission current efficiency can reach 25.9%.As the width of emission surface increased,the emission current efficiency and the emission current per unit area first increased and then decreased.Under the driving voltage of 3 V,the emission current per unit area can reach 50.4?8)~2.In the experiment,it was found that the characteristics of the abrupt PN heterojunction of the Ag thin film electrode sample were destroyed after high temperature thermal cleaning.The Ti/Pt/Au thin film electrode had high thermal stability and was suitable for preparing base electrode of electron-injection cathode.The Ti/Pt/Au thin film electrode samples were subjected to an electrical test similar to electron emission,and the test results were in good agreement with the simulation results.It was predicted that the electron emission test of the Ti/Pt/Au thin film electrode sample would achieve the ideal effect.There were three main reasons why the electron emission test of the Ag thin film electrode sample was not satisfactory:the Ag diffusion after high temperature thermal cleaning;the p-Al GaAs layer and the graded bandgap p-Al GaAs layer were too thick;and the emission surface area was small.