Influence of O, NF ₃ , and Impurity Gases on the Lifetime of NEA GaAs Photocathodes: A Theoretical Research

ABSTRACT Negative electron affinity GaAs photocathode exhibits a relatively limited operational lifetime. The primary factors influencing the lifetime of photocathodes are the desorption of Cs atoms and the interaction between the impurity gas molecules and the photocathode surface. In this manuscript, impurity gas molecules (including H 2 O, CO, and CO 2 ) adsorbed Cs‐only, Cs/O, and Cs/NF 3 activated GaAs(001) β2(2 × 4) models were constructed, the desorption behavior of Cs atoms was investigated using molecular dynamics simulations, whereas the interaction between the impurity molecules and the activated surface was analyzed through density functional theory calculations. Results showed that the introduction of H 2 O and CO 2 would intensify the desorption of Cs, erode the cathode lifetime, O and NF 3 could stabilize the surface Cs atoms, extended the cathode lifetime, slowed down the Cs desorption caused by H 2 O and CO 2 , and also resisted the corrosion of impurity gases. The anticorrosion effect of NF 3 is more obvious than O atom. O and NF 3 could enhance the dipole moment from the surface to the bulk, reduced the work function, and promoted photoelectric emission. Impurity gases could introduce the dipole moment from the bulk to the surface, increased the work function and hindered photoelectric emission.