Stability of negative electron affinity Ga0.37Al0.63As photocathodes in an ultrahigh vacuum system

The stability of negative electron affinity Ga0.37Al0.63As photocathodes in an ultrahigh vacuum system has been investigated. The degraded photocurrents of the Cs/O activated Ga0.37Al0.63As photocathodes under illumination with different intensity are recorded in real time, and the quantum efficiencies are measured after the degradation. The degraded quantum efficiencies of the photocathode under no illumination are measured at regular intervals. Multiple activations are performed on the Ga0.37Al0.63As photocathode, after that the quantum efficiencies and the degraded photocurrents are measured. The results indicate that the lifetime of the Ga0.37Al0.63As photocathode increases as the intensity of illumination decreases, and is longer than that of the GaAs photocathode in the case of no illumination. Besides, the Ga0.37Al0.63As photocathode performed after the second activation would obtain optimal stability.