Negative oxygen vacancies in HfO2 as charge traps in high-k stacks

The optical excitation and thermal ionization energies of oxygen vacancies in m-HfO2 are calculated using a non-local density functional theory with atomic basis sets and periodic supercell. The thermal ionization energies of negatively charged V− and V2− centers are consistent with values obtained by the electrical measurements. The results suggest that negative oxygen vacancies are essentially polaronic in origin. They are likely candidates for intrinsic shallow electron traps in the hafnium based gate stack devices.