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The resolution model of graded doping and graded composition reflection-mode AlGaAs/GaAs photocathode is solved numerically from the two-dimensional continuity equations. According to the model, the theoretical modulation transfer functions (MTFs) of different structure reflection-mode photocathodes were calculated, and the effects of doping concentration, Al composition, AlGaAs and GaAs layer thickness on the resolution of cathodes were analyzed. The simulation results show that both graded composition and graded doping structures can increase the resolution of photocathode, and the effect of graded composition structure is more pronounced. The resolution improvement is attributed to the built-in electric field induced by a graded composition or doping structure. The simulation results also show that the MTFs of cathodes are affected by the AlGaAs and GaAs layer thickness.

The quantum efficiency equations of two kinds of reflcetion-mode GaAs photocathodes (GaAs-GaAs and AlGaAs-GaAs) with back interface recombination velocity have been solved from the diffusion equations. According to these quantum efficiency equations, the integral sensitivities as a function of active layer thickness, electron diffusion length and back interface recombination velocity for both kinds of cathodes are simulated. Through the theoretical simulation, we found the active layer thickness for AlGaAs-GaAs cathodes has an optimum value at which the cathodes achieve the maximum sensitivity. Under most conditions, the theoretical integral sensitivities of AlGaAs-GaAs cathodes are greater than that of GaAs-GaAs cathodes. This is attributed to that AlGaAs-GaAs interface barrier reflects most photoelectrons back into the active layer. The theoretical spectral response of both kinds of cathodes is also simulated. We found that the increase in integral sensitivity of AlGaAs-GaAs cathodes mainly reflects in the increase of spectral response of long wavelength photons.