Fermi level, work function and vacuum level

Abstract

Electronic levels and energies of a solid, such as Fermi level, vacuum level, work function, ionization energy or electron affinity, are of paramount importance for the control of device behavior, charge carrier injection and transport. These levels and quantities, however, depend sensitively on the structure and surface morphology and chemical composition of the solid. A small amount of contaminants on a metal surface, or a shift in molecular orientation at the surface of an organic semiconductor, can change work function and vacuum level position by a large fraction of an electron-volt, and significantly impact the electronic structure of interfaces. The goal of this brief focus article is to provide definitions of key concepts and review simple mechanisms that affect these fundamental quantities.