Ab initio study of structural, vibrational and dielectric properties of high-κ HfO2 as a function of doping

By means of plane-wave pseudopotential techniques we have computed the electronic and the vibrational properties of Hf(1-x)Ge(x)O(2) alloy as a function of Ge concentration in the range 0.0 <= x <= 0.5. By effect of Ge doping the tetragonal distorted fluorite structure, that for zero doping at ambient condition is meta-stable with respect to the monoclinic phase, decreases its energy by effect of doping and becomes energetically favoured at moderate doping concentration. At the same time the c axis of this phase decreases approaching the value of cubic symmetry at about x similar to 0.13. The average of the main component of the dielectric constant decreases as a function of doping up to moderate Ge concentration at which the cubic phase is stabilized by Ge doping; the dielectric constant of this structure (kappa similar to 20) is larger than the one of bulk monoclinic HfO2, but lower than the one predicted of bulk undoped cubic system.