Surface evolution of AlGaN nanowire decorated by cesium atoms: A first principle study

Abstract

Surface decoration with cesium on the photocathode is an effective method to reduce surface barriers and promote electron emission. In this study, we investigated the changes in surface properties of AlGaN nanowire coated with Cs atoms using first-principle calculations. The N bridge site is the most stable site for a single atom deposition. As more Cs atoms are deposited on the surface, the average adsorption energy increases along with the weakened ionization of Cs adatoms. The Bader charge of surface Al and Ga atoms undertake significant changes in comparison with tiny alteration of N atoms, especially for Al atom with a decrease of 0.41 |e|/atom. The variation in surface work function reaches a maximum of 2.3 ∼ 2.5 eV at Cs coverage of 0.5 ∼ 0.75 ML, which can be attributed to the synergistic effect of dipole length and charge redistribution. The donor states underneath CBM induced by the orbital overlap of Al-p, Ga-p and Cs-d electrons accompanied by the downward band bending in the band structures. This work provides theoretical insight into the surface evolution of Cs-decorated AlGaN nanowires and offers guidance for the development of state-of-the-art nanostructured vacuum devices.