|DATE||January 04 (Thu), 2018|
|INSTITUTE||Rensselaer Polytechnic Institute, USA|
|TITLE||What is built-in potential?|
The built-in potential is the potential difference due to the electric dipole at the interface of two dissimilar materials. It is of central importance to the understanding of many phenomena in electrochemistry, electrical engineering, and materials science because it determines the band alignment at the interfaces. Despite its importance, its exact sign and magnitude have generally been recognized as an ill-defined quantity for more than half a century. Here, we provide a universal definition of the built-in potential. The key to our finding is identifying the common energy reference between dissimilar bulk materials, which overcomes the fundamental limitations of traditional approaches. Furthermore, we find that the built-in potential is explicitly determined by the bulk (i.e., innate) properties of the constituent materials when the system is in electronic equilibrium, while the interface plays a role only in the absence of equilibrium. Our quantitative theory enables a unified description of a variety of important properties in all types of interfaces, ranging from work functions and Schottky barriers in electronic devices to electrode potentials and redox potentials in electrochemical cells. Beyond the interfacial physics, the insight into the common energy reference of bulk solids provides clues for understanding the long-standing problem of defining an average electrostatic potential of infinitely large systems, which could lead to a precise determination of the absolute deformation potentials and formation energies of charged defects in bulk.