Photoemission mechanism of GaN photocathode:a first-principle study

To explore the photoemission mechanism of GaN photocathode and make clear the role played by the intrinsic gallium oxide at GaN surface, the Ga-O-Cs model was built and the properties of adsorption energies, mulliken charge distribution, work functions and density of states were calculated with the first-principle density functional theory(DFT).By calculating the surface adsorption energies of different models, we know that all the surface adsorption energies are negative, and the models are reasonable. The work function results indicate that although first connection of oxygen atom with gallium atom will lead to much higher value enhancement, while the subsequent deposition of cesium atom will achieve more decrease of work function to achieve NEA status. The calculated work functions are in good coordinate with experimental photocurrent change with different coverage. Meanwhile, the tested electron affinity variations are reasonably explained with the proposed and calculated Ga-O-Cs model. These calculations supply a theoretical evidence of the photoemission mechanism of GaN photocathodes, which would direct the following GaN and AlGaN photocathodes preparation technique.