A density functional theory research on Cs–O activation process of GaAlAs photocathodes

Abstract

Using plane-wave ultrasoft pseudopotential based on first-principles, the Cs–O activation process of GaAlAs photocathodes is investigated. In the Cs–O alternate activation process, Cs–O unit is inclined to form the Cs-outer structure. After the adsorption of O atom, the additional O atoms weaken the dipole between Cs atoms and β 2 (2 × 4) surface and introduce additional dipole between Cs and O. Dual-dipole model is used to express the variation tendency of dipole moment and work function. During activation process, electrons of Cs atoms offset to the surface, the additional electrons at the surface cause n-type surface state, and result in downwards band bending; at the same time, the vacuum level is gradually lowered, forming two potential barriers. An experiment is performed and the photocurrent curve is well consistent with the calculation results. After Zn doping, the work function near Zn atoms is lower than surrounding, causing the scale-like effect.