Surface activation behavior of negative-electron-affinity exponential-doping GaAs photocathodes

In view of the effect of doping structure on the surface activation behavior, the Cs–O activation experiments under the same preparation condition were performed on the exponential-doping and uniform-doping GaAs photocathodes. The activation results show that, compared with the uniform-doping photocathode, the exponential-doping photocathode presents a lower photocurrent peak after the initial Cs activation and a higher photocurrent peak after the Cs–O alternate activation. Based on the double dipole model, the parameters of surface potential barrier are obtained from the calculation of longitudinal energy distribution of emitted electrons according to the ratio of photocurrent peak after Cs–O activation to that after Cs activation. The discrepancy in the photocurrent evolution during the entire activation process is related to the different variations in surface potential barrier profile.