Epitaxial anatase HfO2 on high-mobility substrate for ultra-scaled CMOS devices

On the basis of ab initio simulations, the formation of an epitaxial phase that has the anatase structure has been proposed as the microscopic mechanism responsible for the preferential orientation of monoclinic HfO2 films on the high-mobility (0 0 1) oriented Ge and GaAs substrates. In fact, the oriented monoclinic structure follows the in-plane axis of the anatase phase as proved by X-ray scattering measurements. The fact that epitaxial HfO2 anatase has no bulk counterpart is explained by our calculations as due to the unfavorable Helmholtz free energy of anatase phase when the condition of epitaxy is released.