Extra hole threshold in HfO₂ ferroelectric phase stabilization

Understanding ferroelectric phase stability in hafnium-based oxides is crucial for high-quality thin-film fabrication and device applications. Multiple strategies stabilize the phase, with evidence highlighting extra holes’ key role. However, research on extra holes’ impact on ferroelectric phase stabilization remains inadequate. This study combines first-principles calculations with experimental data, identifying a critical extra-hole concentration threshold (0.3 h/f.u.) for HfO₂ ferroelectric phase stabilization. We designed two coordinated experiments to verify the extra-hole threshold in HfO₂. Using SrRuO₃ (SRO) as the bottom electrode, we studied three HfO₂ systems (Sm, Eu, and La doped). All systems showed optimal ferroelectric performance at 7.5% doping. Our results also showed that HfO₂ films on Sm-doped (La_0.67Sr_0.33MnO₃) LSMO (5.5% doping) achieve optimal polarization, comparable to SRO (7.5%). These mutually corroborative experimental and theoretical results indicate that the extra-hole threshold optimizes HfO₂ ferroelectric thin film growth and facilitates its electronic device applications.