Electronic states and Schottky barrier height at metal/MgO(100) interfaces

Using an ab initio total energy approach, we study the electronic structure of metal/MgO(100) interfaces. By considering simple and transition metals, different adsorption sites and different interface separations, we analyze the influence of the character of metal and of the detailed interfacial atomic structure. We calculate the interface density of states, electron transfer, electric dipole, and the Schottky barrier height. We characterize three types of electronic states: states due to chemical bonding which appear at well defined energies, conventional metal-induced gap states associated to a smooth density of states in the MgO gap region, and metal band distortions due to polarization by the electrostatic field of the ionic substrate. We point out that, with respect to the extended Schottky limit, the interface formation yields an electric dipole mainly determined by the substrate characteristics. Indeed, the metal-dependent contributions (interfacial states and electron transfer) remain small with respect to the metal polarization induced by the substrate electrostatic field.