On mechanism of phase stabilization in ferroelectric and high- <i>k</i> HfO2

Abstract

We present a systematic first-principles study of dopant-induced phase stabilization in HfO2 across ferroelectric (FE) and non-ferroelectric polymorphs for a large set of dopants. To overcome the strong configuration dependence of defect energetics, we develop a multi-stage screening workflow that identifies low-energy dopant–vacancy configurations. In an equilibrated-solution [“PVD” (physical vapor deposition)] model, bulk T = 0 K energetics indicate that ionically compensated doping alone is insufficient to stabilize the orthorhombic-ferroelectric phase over the monoclinic phase; certain dopants even increase its relative energy. Configurational-entropy corrections are small at device-relevant temperatures, and vibrational contributions—benchmarked against explicit phonon calculations—primarily stabilize the tetragonal phase, remaining inadequate to reverse bulk phase ordering at moderate anneal temperatures. We further observe that many rhombohedral-FE supercells lose phase identity upon relaxation, typically collapsing toward orthorhombic-FE motifs, underscoring sensitivity to local defect arrangements. To assess deposition effects, we introduce a planar (“atomic layer deposition”) model that mimics dopant layering; it amplifies dopant-identity sensitivity and can reshape phase competition compared to the equilibrated-solution limit. Overall, our results suggest that experimentally observed ferroelectric stabilization in thin films arises from a combination of interfacial/finite-size terms and deposition-induced dopant distributions, rather than bulk thermodynamics alone.