Effect of electron lateral diffusion in the reflection-mode exponential-doping GaAlAs photocathode on resolution

Resolution of a reflection-mode GaAlAs photocathode which is efficiently characterized by modulation transfer function (MTF) is primarily governed by electron lateral diffusion in this photocathode. As several crucial parameters for the GaAlAs photocathode, the length of electron diffusion L-D, the thickness of emission layer T-e, the coefficient of optical absorption alpha, and the recombination velocity at back-interface S-V has a significant effect on the degree of lateral diffusion. To obtain a high resolution, by establishing an appropriate model of MTF for reflection-mode exponential-doping GaAlAs photocathode, the effect of L-D, T-e, alpha, and S-V on corresponding MTF and quantum efficiency for exponential-doping and uniform-doping Ga0.37Al0.63As photocathodes has been researched in detail. And then we have discussed the dependence of electron lateral diffusion on L-D, T-e, alpha, and S-V. The calculated results demonstrate that the reflection-mode exponential-doping Ga0.37Al0.63As photocathode has a great potentiality in achieving high resolution and high quantum efficiency, compared with its counterpart employed uniform-doping structure. It is mainly because that electron lateral diffusion in this photocathode is bound by electric field which is formed by exponential-doping structure. In practice, for a given reflection-mode exponential-doping Ga0.37Al0.63As photocathode, a compromise between high resolution and high quantum efficiency must be made.