Grazing incidence X-ray diffraction (GIXRD) data have indicated that the orthorhombic \(Pmn{{2}_{1}}\) phase previously detected in a 10–20 nm buried ferroelectric HfO2:Al2O3 (10:1) layer of silicon-on-insulator and silicon-on-sapphire structures after annealing at \(T > 950\) °C for 1 h is absent after 30 s stepwise rapid thermal annealing treatments. Instead, stressed textured ferroelectric layers thermally stable up to 1000°C are formed with the {111} and {002} orientations for silicon and sapphire substrates, respectively, in the rhombohedral r \(R3\) or orthorhombic \(Pca{{2}_{1}}\) phases, which are not manifested in GIXRD patterns. The high remnant polarization in silicon-on-insulator structures indicates that the rhombohedral r \(R3\) phase is favorable.
