Research on surface phase transformation of NEA GaAs photocathodes during the high-temperature cleaning process

In this manuscript, a high-temperature cleaning experiment was carried out, according to the measurement results of Quadrupole Mass Spectrometer (QMS), and it was concluded that 5-phase transformation reactions took place in the process of high-temperature cleaning. According to the experiment, 10 adsorbed surface models were built, using first-principles calculation method, and the energy and electronic structure of these models were researched. Gibbs free energy results showed that 5-phase transformations could take place spontaneously, and adsorption energy results showed that the phase transformations were conducive to the desorption of impurity oxides. Mulliken bond population results were used to analyze the change of bonding during the phase transformations. PDOS results showed that during the phase transformations, s state and p state of the involved As(Ga) atom changed obviously. Electron density difference was used to analyze the electron distribution during the phase transformations, and dipole moment results showed that during the phase transformation, the charge offset amount and distance were changed, causing the change of work function and the photoemission of the surface.