Computational investigation of the phase stability and the electronic properties for Gd-doped HfO_2

Rare earth doping is an important approach to improve the desired properties of high-k gate dielectric oxides. We have carried out a comprehensive theoretical investigation on the phase stability, band gap, formation of oxygen vacancies, and dielectric properties for the Gd-doped HfO_2. Our calculated results indicate that the tetragonal phase is more stable than the monoclinic phase when the Gd doping concentration is greater than 15.5%, which is in a good agreement with the experimental observations. The dopant's geometric effect is mainly responsible for the phase stability. The Gd doping enlarges the band gap of the material. The dielectric constant for the Gd-doped HfO_2 is in the range of 20–30 that is suitable for high-k dielectric applications. The neutral oxygen vacancy formation energy is 3.2 eV lower in the doped material than in pure HfO_2. We explain the experimental observation on the decrease of photoluminescence intensities in the Gd-doped HfO_2 according to forming the dopant-oxygen vacancy complexes