Structural and vibrational properties of high-dielectric oxides, HfO2 and TiO2: A comparative study

Within the framework of density functional theory, we have computed structural and vibrational properties of high-κ dielectric oxides, HfO₂ and TiO₂. We have considered different polytypes of these oxides and computed the corresponding static dielectric constants in order to investigate what are the more promising materials suitable for technological application. We found the flourite phase of hafnium dioxide, that is a promising candidate as gate oxide in ultra-scaled complementary metal-oxide-semiconductor (CMOS) technology, is structurally unstable due to the presence of soft phonon modes that have wave-vectors in the region of the Brillouin zone containing the K- and X-points. According to our results, the fluorite TiO₂ is structurally unstable as well but, contrary to HfO₂, the soft phonon modes have wave-vectors in the whole Brilouin zone. Calculations of the thermodynamical properties of the baddeleyite HfO₂, the stable phase at ambient condition, complete the work.