Atomistic calculation of leakage current through ultra-thin metal-oxide barriers

We investigate the effect of O vacancies and B interstitial on the leakage current through monoclinic HfO₂. Transport is calculated from a combination of first-principles molecular dynamics simulation using local-orbital density functional theory, and non-perturbative scattering theory. Five different defects were considered: (1) O vacancy at a three- and (2) a four-coordinated O site located in the HfO₂ region, (3) O vacancy along a Hf-O-Si bond and (4) along a Si-O-Si bond at the Si/HfO₂ interface, and (5) an interstitial B atom in the HfO₂ region. Bulk vacancies decrease the leakage current because they act as hole, not electron traps, while an interface vacancy along the Si-O-Si bond has a minor effect on the leakage. On the other hand, a vacancy along the Hf-O-Si bond creates states in the Si band gap that strongly enhance the leakage current at a low bias. The presence of an interstitial B atom in bulk HfO₂ enhances the leakage current possibly through a resonant tunneling mechanism.