First-Principles Investigation of the Structure, Energetics, and Electronic Properties of Ru/HfO2 Interfaces

Abstract

The electronic properties of metal oxide semiconductor gate electrodes are strong functions of the structure of the metal−dielectric interface. We use density functional theory to investigate the structures, energetics, and electronic properties of Ru/HfO2 interfaces. We find that atom-by-atom deposited Ru films have significantly different interfacial structures from epitaxially connected Ru films on the m-HfO2(001) surface. Atom-by-atom deposited films are rougher than epitaxially connected films, even when forced to form two-dimensional films. These interfacial structural differences lead to differences in the electronic properties of the films and therefore affect electrical properties, such as the work function of the gate electrode. We found that for both types of films the partial densities of states of interfacial layers are significantly different from that of the bulk region. Each shows charge transfer from the interfacial Ru layer to the interfacial dielectric layer, although the magnitude of charge transfer varies. Thus both films exhibit metal induced gap states in the band gap region of the interface localized on atoms of the HfO2 interfacial layer.