Study of cesium and oxygen adsorption on surface of GaAlAs photocathode in ultra-high vacuum chamber

The mechanism of cesium (Cs) and oxygen (O) adsorption on GaAlAs photocathode has been investigated. The models of Cs and O adsorption on GaAlAs surface are studied, and the electron affinity changing with Cs coverage on GaAlAs surface is calculated based on Topping model. The experiments of Cs activation on GaAlAs and GaAs are performed, and the Cs, O activation experiments with different heat cleaning temperatures are performed on GaAlAs photocathodes. The photocurrent and spectral response curves in the experiments are measured and analyzed. The results show that the Topping calculation of electron affinity changing with Cs coverage on GaAlAs surface is in consistent with the result of experiment, and the electron affinity nearly reaches the bottom of conduction band after the Cs activation. The GaAlAs phtocathode treated by 700 °C heat cleaning could obtain a good photoemission performance after Cs, O activation.