Quantum efficiency of transmission-mode AlxGa1−xAs/GaAs photocathodes with graded-composition and exponential-doping structure

• Quantum efficiency model of complex AlxGa1−xAs/GaAs photocathode structure is deduced.
• Structure with twofold built-in electric fields notably improves cathode performance.
• The photoemission performance is related to Al proportion and cathode thickness.

A transmission-mode AlxGa1−xAs/GaAs photocathode with the combination of composition-graded AlxGa1−xAs window layer and exponential-doping GaAs emission layer is developed to maximize the cathode performance. The theoretical quantum efficiency model with this complex structure containing twofold built-in electric fields is deduced by solving the one dimensional continuity equations combined with the three-step model. By comparison of spectral characteristics of photocathodes with different composition and doping structures, and through analysis of cathode structure parameters, it is found that the twofold built-in electric fields can effectively improve photoemission performance of AlxGa1−xAs/GaAs photocathode, which is related to Al proportion variation range and thicknesses of window layer and emission layer. The quantum efficiency model would provide theoretical guidance for better design of transmission-mode graded bandgap photocathodes.