Structural and energetic origin of defects at the interface between germanium and a high- k dielectric from first principles

Atomic-scale models of the abrupt high- k/Ge interface with a range of suboxide stoichiometries GeO_x are presented and compared to their Si analogs. Molecular dynamics and geometry optimization were carried out at the density functional theory level to yield structures and energetics. Cohesion across the interface becomes stronger with increasing oxidation of the Ge suboxide. Three-coordinate Ge is identified as the main defect and is formed at low energetic cost, which accounts for the observed abundance of defects at oxide/Ge interfaces. The optimum low temperature interface is defect-free, predominantly Ge²⁺ with some Ge⁺.