Epitaxial phase of hafnium dioxide for ultrascaled electronics

We propose a mechanism leading to the local epitaxy observed in HfO2 films grown on Ge(001). Our model is based on state-of-the-art ab initio calculations compared with available experimental data. According to the proposed model, the observed preferential orientation of the monoclinic structure is related to the relaxation of the epitaxially stabilized anatase phase when a critical thickness is reached. In fact, the preferential orientation of the monoclinic structure follows the in-plane axis of the anatase phase, as proven by accurate x-ray scattering data. We predict that the anatase phase, which has no bulk counterpart and has a calculated dielectric constant comparable to the bulk monoclinic one, is almost lattice matched with the Ge(001) substrate. Although the observation of the anatase phase is still missing, its stabilization would allow a control at the atomic level of the HfO2/Ge(001) interface, possibly providing better performances in the next generation complementary-metal-oxide-semiconductor devices.