Ab initio study of charge trapping and dielectric properties of Ti-doped HfO2

The electronic structure and relative stability of monoclinic, tetragonal, and cubic phases of HfO2 with Ti doping in the range of 3.125%-37.5% are studied by means of first-principles calculations. The dielectric response, and electron and hole trapping properties of Ti-doped monoclinic HfO2 are calculated using a hybrid density-functional B3LYP. The incorporation of Ti into HfO2 induces higher polarizability of Hf and O ions, accompanied by an increase in the static dielectric constant and softening of phonon modes. However, the Ti ions serve as deep electron traps inducing localized levels in the gap and, at high Ti concentrations, the HfO2 conduction-band offset with Si is effectively reduced by about 1.5 eV.