Strain Control of (001)-Polar-Axis-Oriented Epitaxial Y-Doped HfO2 Thin Films

{100}-Oriented epitaxial orthorhombic (Hf0.93Y0.07)O2 (7YHO) films were grown at 700 °C on various substrates, with and without (Ce0.35Zr0.65)O2 (CZO) buffer layers, by using pulsed laser deposition. The crystal phase and orientation were determined by X-ray diffraction. The long axis [100] or short axis [010]/[001] orientations were controlled by lattice matching. Nearly relaxed epitaxial orthorhombic (100) 7YHO films on LaAlO3 and SrRuO3/SrTiO3 substrates were obtained, and their unclamped lattice constants were experimentally observed. The in-plane lattice parameter of the (010)/(001)-oriented 7YHO films obtained by using the CZO buffer layers was within the range of 0.518–0.523 nm. This study demonstrates selective growth and lattice strain control with respect to the in-plane lattice spacing of the underlying layers. These findings provide further possibilities for understanding the fundamental ferroelectric properties of HfO2-based materials.