Effect of Surface Barrier on Electron Escape Probability of Gradient-doping GaN Photocathode

By calculating energy distribution of gradient-doping GaN photocathode, the effect of surface barrier on electron escape probability of this photocathode has been studied. The calculated results show that gradient-doping GaN photocathode can obtain higher escape probability, compared with uniform-doping one. Moreover, barrier I has a significant influence on escape probability, whereas barrier II has a minor one. In order to verify this theoretical result, the photocurrent of two GaN photocathode samples has been measured by a multi-information-test system. The Experimental results show that gradient-doping GaN photocathode has a higher escape probability than uniform-doping one. And evident influence of barrier I with Cs-activation only on escape probability can be obtained, whereas little influence of barrier II with Cs/O-joint-activation is found.