Improved performance of GaAs photocathodes using effective activation technique

To achieve negative-electron-affinity state, the atomically clean surface of GaAs-based photocathode is usually activated by cesium and oxygen in the ultrahigh vacuum environment. In view of the required computer-control of evaporation flow rates, the solid oxygen dispenser instead of gaseous oxygen is urgently needed just as the regular cesium dispenser. Accordingly, the solid cesium and oxygen dispensers were applied to activate epitaxial GaAs cathode samples. Two types of solid oxygen dispensers composed of barium peroxide powder and silver oxide powder respectively are employed to improve cathode photoemission performance. The experimental results show that the barium peroxidebased oxygen dispenser can release more oxygen and bring in higher activation photocurrent and spectral response than the silver oxide-based one. The unsatisfactory feature is that the silver oxide-based oxygen dispenser released effectual oxygen gas more slowly than the barium peroxide-based oxygen dispenser. Therefore, an effective activation technique was proposed to ameliorate this unfavorable phenomenon for the silver oxide-based dispenser, which can bring out the desired symmetry of photocurrent curve shape during the Cs/O alternate activation process. The improved activation technique would provide guidance for the optimization of activation craft.