Quantum efficiency decay mechanism of NEA GaN photocathode： A first-principles research

Using the first-principles method based on the density functional theory(DFT), the work function of seven different Ga N(0001) e1 × 1T surface models is calculated. The calculation results show that the optimal ratio of Cs to O for activation is between 3∶1 and 4∶1. Then, Cs/O activation and stability testing experiments on reflection-mode negative electron affinity Ga N photocathodes are performed. The surface model [Ga N(Mg): Cs]Cs-O after being activated with cesium and oxygen is used. The experiment results illustrate that the adsorption of O contained in the residual gas increases the surface potential barrier and the reduction of the effective dipole quantity is the basic cause of the quantum efficiency decay.