Cs and O co-adsorption on p-type Al_0.5Ga_0.5N specialIntscript UV photocathode surface

In the study, the co-adsorption of Cs and O atoms on p-type Al0.5Ga0.5N specialIntscript surface was firstly calculated. The adsorption became unstable and the surface structure was deformed when the adsorption of Cs was at 0.75 monolayer coverage. The adsorption stability and surface structure were improved after oxygen adsorption on Cs-covered surface. In the stage of Cs and O co-adsorption, after the adsorption of 2Cs2O, two O atoms form dioxygen. After the adsorption of 3Cs2O, two O atoms were independent from each other. One O atom was in the outermost layer and the dipole moment pointing to the outside of the surface was formed and thus hindered the escape of photoelectron. In Cs and O co-adsorption, after Cs was further adsorbed, the adsorbed atoms of 2Cs2O1Cs and surface atoms formed the three-staged dipole moment. Both the largest dipole moment and the smallest work function were achieved for the surface. The negative electron affinity was realized due to the downward shift of the conduction band and the upward shift of the valence band. The surface adsorption peak at 177.16 nm met the requirements for ultraviolet detection.