Study On Material Properties Of GaAs Photocathode Based On Vacuum Channel Structure

With the rapid development of micro-nanotechnology and micro-nanofabrication processes,surface micro-nanostructures have attracted widespread concern in various solidstate along with vacuum optoelectronic devices and are expected to be a breakthrough in enhancing the performance of GaAs photocathodes utilized in electron sources.In this paper,in-depth researches are executed from the perspective of photoelectric emission theory,quantum efficiency theory,field emission theory and preparation process of vacuum channel photocathode to design a structure that can realize absorption enhancement and analyze the related photoelectric emission properties,in order to explore the approaches to enhance the performance of GaAs photocathodes from theoretical simulation and structural design,effects of laser power and pulse width on electron emission are studied.The main works are as follows:(1)The optical simulation model of the vacuum channel GaAs cathode structure is built and effects of different structure vacuum channels on the surface optical properties are numerically simulated using the time-domain finite difference method.After comparing different shape models,the rectangular channel with better absorption enhancement characteristics is selected as the optimized model in the later consideration,and the effects of different duty cycles,diameters and channel shapes on the optical properties of the cathode assembly are analyzed.(2)The electrical simulation model of the vacuum channel is built to further illustrate the effect of vacuum trench shape on photoelectric emission using electric field energy distribution and electron distribution diagram.The results show that the electric field intensity at the surface of the cathode material is lower in the area away from the edge of the vacuum channel.Also,the closer from the middle of the vacuum channel,the more difficult it is for electrons to break through the surface barrier and escape into the vacuum.(3)The light-modulated vacuum channel photocathode assemblies are prepared without activation experimentally.Using microelectronic processing technology,the GaAs cathode surface is laminated by films and the vacuum channel structure is prepared using etching process.An electron emission test system are built to test the effects of different laser power and pulse width on the performance of the photocathode assemblies.Limited by the photoelectric conversion efficiency of the material,laser power and pulse width have no significant effect on the photocathode emission current.The pulsed emission current of the prepared vacuum channel GaAs photocathode without activation is 1.5×106 V/cm at a gate voltage of 30 V,and the emission current density of the cathode assembly reaches 0.582 A/cm~2.