Effect of graded bandgap structure on photoelectric performance of transmission-mode AlGaAs/GaAs photocathode modules.

The graded bandgap AlGaAs/GaAs photocathode with graded composition and exponential doping structure has shown great potential for improving photoemission capability. In order to better study the performance of transmission-mode AlGaAs/GaAs photocathode with the complex graded bandgap structure, the experimental optical properties and quantum efficiency are measured by comparison with uniform composition and exponential doping AlGaAs/GaAs photocathode. The theoretical optical properties of the multilayer AlGaAs/GaAs photocathode modules are calculated by matrix formula on the basis of thin-film optical principles. The effect of cathode thickness and aluminum proportion on optical properties are analyzed by simulation. The results show that these parameters have complicated effects on the optical properties. Different parameters are presented as the changes of peak and valley of the optical property curves. Meanwhile, the emission layer has a significant effect on the absorptivity values of the photocathode modules, which will obviously influence photoemission performance. By using the optical properties via calculation, a better fit of the experimental data with the theoretical model can be achieved, which would make reasonable guidance for further investigation of these complex graded bandgap photoemitters.