Electronic–Structural Phase Correlations in Oxygen‐Deficient Hafnia Nanocrystals

Abstract Layers of HfO ₂ and (Hf,Zr)O ₂ crystalline nano‐particles are synthesized via direct liquid injection atomic layer deposition, and a comprehensive set of structural, chemical, and electrical characterizations is employed to elucidate their phase composition and functional behavior. X‐ray photoelectron spectroscopy revealed a compositional contrast between the films: (Hf,Zr)O ₂ layers contained up to 45% stoichiometric oxide, while pure HfO ₂ films are dominated by sub‐oxides, especially under strongly reducing conditions, in which exclusively sub‐oxide phases and p‐type semiconducting behavior is revealed. Electrical measurements indicated room‐temperature stabilization of polar phases and tetragonal‐to‐orthorhombic phase transition with a Curie temperature near 200 K. FTIR spectroscopy confirmed the presence of tetragonal and orthorhombic HfO ₂ phases, providing insight into minor features observed ≈30° (2θ) in X‐ray diffraction patterns. Notably, devices incorporating an AlN interlayer demonstrated a significant enhancement in pyroelectric performance, suggesting this strategy to advance the pyroelectric performance of HfO ₂ ‐based materials, supporting their development for lead‐free sensor technologies.