Modelling Photocathode Performance using Density Functional Theory

The structure and composition of a crystalline material can strongly affect electronic properties such as the electron affinity and the work function. By optimising the properties of the material, it is possible to design photocathodes for a wide range of applications. Molecular beam epitaxy (MBE) provides much improved control over the composition and synthesis of a photocathode versus traditional manufacturing methods. In this paper, we verify the application and reliability of density functional theory (DFT) to model photocathode performance by comparing simulations of dicaesium telluride- and gallium arsenide-like structures to other simulated and experimental results. DFT modelling was carried out using MEDEA-VASP software, with verification achieved for simulations of the band structure and density of states. This enables ongoing simulations to optimise photocathode materials with regards to properties including electron affinity and absorption coefficient.

I. Introduction

MATERIALS such as dicaesium telluride (Cs₂Te) and gallium arsenide (GaAs) are examples of photocathodes at either end of the visible spectrum, with a wide range of applications, e.g. in defence, security and remote sensing. One route to manufacturing these materials is through molecular beam epitaxy (MBE) [1], which gives significant control over the stoichiometry and crystallinity of the photocathode material. Varying the stoichiometry, and properties of the crystal structure such as the Miller index, can have a significant effect on the work function, the band structure and the electron affinity. By identifying the ideal material properties for a photocathode, MBE can be used to synthesise this material.