Density Functional Theory Calculations of Al doped Hafnia for Different Crystal Symmetry Configurations

Thin films of Hf based oxides gained importance after the discovery of the ferroelectricity in these materials¹. One of the ways to achieve ferroelectricity in HfO₂ is doping with metals such as Zr and Al to modify the crystal structure towards orthorhombic symmetry. In Hf based oxide thin films prepared by doping, multiple crystal phases could emerge. In this work, we theoretically investigated the stability of the possible structures that could be present in Al doped HfO₂ using quantum mechanical methods. Specifically, using plane wave density functional theory, the monoclinic, tetragonal, orthorhombic, and rhombohedral phases of aluminum doped hafnia were geometrically optimized. The resulting equilibrium structures for 3%, 6%, and 7% Al doped hafnia structures will be used as theoretical reference structures for EXAFS spectra obtained Al doped HfO₂ thin films_.

Keywords: Density functional theory, ferroelectricity, doped hafnia

¹T. S. Boscke, J. Muller, D. Brauhaus, U. Schroder, and U. Bottger, Appl. Phys. Lett. 99, 102903 (2011).