Atomic mechanism of flat-band voltage shifts at La2O3, Al2O3 and Nb2O5 capping layers

We provide the first fully atomistic model of the origin of the flat band voltage shifts due to La- and Al-based capping layers, which are frequently used to control the flat band voltage in high K metal gate stacks. Supercells with substitutional La, Sr, Al or Nb at an HfO2–SiO2 interface create dipole layers which shift the flat band voltage in the observed direction. The shift only occurs for substitutions at the interface, not distributed over the HfO2 layer. The shift is due to an image charge effect combining the metal electronegativity and oxygen density.