Modeling photocathode stoichiometric effects on quantum efficiency

Abstract

Useful models of quantum efficiency (QE) for growth characterization but also simulation require material and optical parameters that exhibit complex dependencies on frequency and composition. We combine a Moments model of QE with a Lorentz–Drude–Resonant (LDR) model for metals and its extension to an Adachi–Drude–Resonant (ADR) model for semiconductors for the optical parameters based on density functional theory (DFT) simulations. A rapid numerical implementation is developed for characterization studies that will be advantageous in simulating particle accelerators and Free Electron Lasers using particle-in-cell codes. Changes in stoichiometry are then related to variations in QE, reflectivity, and laser penetration depth as governed by the ADR parameterization for alkali antimonide materials compared to a baseline DFT simulation of Cs3Sb. The correlation between LDR/ADR parameters and stoichiometry allows for an modifiable parameter library enabling user alterations for simulations to explore the effects of changes in composition or to compare/contrast different photocathode bulk materials in beam optics codes.