The evolution of GaN photocathode surface barrier before and after activation

Using the activation and evaluation system for negative electron affinity (NEA) photocathode, the Cs activation was finished for GaN photocathode, and the Cs, O activations was completed by using the alternate method of Cs source continues, O source intermittent for the cathode sample, the photocurrent curve was gotten during the activation process. Based on the characteristics of NEA and the formation of cathode surface barrier, the evolution of GaN photocathode surface barrier before and after activation was analyzed. After the GaN photocathode being purified, the adsorption of cesium is a key step for getting the NEA surface. With Cs alone, the electron affinity potential change of 3.0eV can be obtained, and the vacuum energy level can be moved to approximately 1.0eV below the bottom of conduction band. Together with Cs, O processing can further reduce the vacuum energy level by 0.2eV.