Defect energy levels in HfO2

The energy levels of the oxygen vacancy and oxygen interstitial defects in HfO2 are calculated using density functional methods that do not need an empirical bandgap correction. The levels are aligned to those of the Si channel using the known band offsets. The oxygen vacancy gives an energy level nearer the HfO2 conduction band and just above the Si gap, depending on its charge state. It is identified as the main electron trap in HfO2. The oxygen interstitial gives levels just above the oxide valence band.