Comparative study on structure and electronic properties of Al0.5Ga0.5N thin film and nanowire photocathode under surface oxidation

Abstract

Oxidation will generate higher surface barriers and new surface states, resulting in declined electron escape probability and electron emission performance, which seriously affects surface activation effect of the photocathode. In order to explore the effects of oxidation on Al0.5Ga0.5N thin film photocathodes and nanowire photocathodes, we have analyzed structure and electronic properties of Al0.5Ga0.5N thin film and nanowire under oxidation. The results show that formation energies of Al0.5Ga0.5N film oxidation surface is negative in both O-rich and O-poor conditions under O adsorption, indicating that surface of Al0.5Ga0.5N film is easily oxidized. However, Al0.5Ga0.5N nanowires are easily oxidized only when O concentration is higher. The formation energies of oxygen substitution model are all positive, indicating that this form of oxide is not easy to form on the surface. The results of band structure and PDOS indicate that pristine Al0.5Ga0.5N film has abundant surface states near the Fermi level. After oxygen adsorption, Ga atoms form stable Ga–O bonds with O atoms and the surface states are weakened. For oxygen substitutional oxidation, compared to Al0.5Ga0.5N thin film, conduction band of Al0.5Ga0.5N nanowire splits to form more energy levels and CBM moves downward, forming an n-type surface, which is not conducive to photoelectric emission.