Hf defects in c-Si and their importance for the HfO2/Si interface:: Density-functional calculations

We have studied, using ab initio density functional theory calculations, substitutional and interstitial Hf impurities in c-Si, for various charge states. Our results indicate that (1) the tetrahedral interstitial defect is energetically more favorable than the substitutional and (2) there are various stable charge states in the Si gap. The possible presence of these charged impurities in the Si channel of HfO2/Si-based metal-oxide-semiconductor devices could lead to a mobility reduction, due to Coulombic scattering.