Differences in stability and repeatability between GaAs and GaAlAs photocathodes

Abstract

For the applications in vacuum photodetectors and photoinjectors, a crucial limiting factor for conventional GaAs photocathodes is the limited lifetime, depending on the Cs–O activation layer vulnerable to the harmful residual gases. In order to develop a type of GaAs-based photocathode with good stability and repeatability, Cs/O activation and multiple recesiation experiments under the same preparation condition were performed on reflection-mode exponential-doped GaAs and GaAlAs photocathodes grown by metalorganic vapor phase epitaxy, and quantum efficiency and photocurrent decay were measured after activation and recesiation. The experimental results show that the photoemission characteristics on cathode degradation and repeatability are different between GaAs and GaAlAs photocathodes. In an unsatisfactory vacuum system, the operational lifetime for GaAlAs photocathode is nearly twice longer than that for GaAs photocathode after Cs/O activation under a high intensity illumination. After multiple recesiations, the quantum efficiency and operational lifetime for GaAlAs photocathode remain nearly unchanged, while those for GaAs photocathode become lower and lower with the increase of recesiation cycles, which reflects the superiority in stability and repeatability for GaAlAs photocathode in contrast to GaAs photocathode operating in the poor vacuum environment.