Performance simulation of reflection-mode GaAs photocathodes with back-interface recombination

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.