Defect energy states in high‐K gate oxides

The electrical energy levels of the different charge states of the oxygen vacancy and the oxygen interstitial in HfO 2 are calculated, using density functional methods which do not need a band gap correction. Lattice distortions around the defect sites produce substantial shifts in the energy levels. The energy levels are aligned to those of the Si channel. In HfO 2 , the oxygen vacancy gives an energy level in the Si gap or just above the gap, depending on its charge state. The O vacancy is identified as the main electrically active defect and trap. The oxygen interstitial gives levels just above the oxide valence band, and the neutral interstitial also gives a level near the Si conduction band. The defect wavefunctions are given. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)