Resolution properties of reflection-mode exponential-doping GaAs photocathodes

Resolution properties of reflection-mode exponential-doping and uniform-doping GaAs photocathodes were calculated and comparatively analyzed by using the modulation transfer function obtained by establishing and solving the two-dimensional continuity equation. The calculated results show that compared with the uniform-doping GaAs photocathode, the exponential-doping structure can improve significantly not only the resolution, but also the quantum efficiency of the photocathode. This improvement differs from the approach for achieving high resolution by reducing the emitting layer thickness TeTe and the electron diffusion length LDLD or by increasing the recombination velocity of back-interface SVSV, which results in low quantum efficiency. Furthermore, the improvement of resolution and quantum efficiency of the reflection-mode exponential-doping GaAs photocathode is due the effect of the built-in electric field on electron transport and on lateral diffusion.