Structural properties and electronic structure of HfO₂ -ZrO ₂ composite films

This study examined the structural evolution of ultrathin Hf _1-xZr_xO₂ composite films with various mixing ratios (x=0,0.1,0.3,0.5,0.7,0.9,1) prepared by atomic layer deposition using x-ray photoelectron spectroscopy (XPS), x-ray absorption spectroscopy (XAS), and x-ray absorption fine structure (XAFS) analysis. As the relative Zr concentration (x) was increased, the composite films underwent a martensitic transition from monoclinic to tetragonal crystal structures near x=0.5-0.7. ZrK - and Hf L₃ -edge XAFS revealed a change in the local structures near the Zr and Hf atoms with changes in the crystal structure. At a low Zr content (x≤0.5), the next-nearest-neighbor coordination in the monoclinic (m) local structure showed significant structural disorder due to diverse structural reconstruction from the tetragonal (t) local structure. Combined XPS and OK -edge XAS studies revealed a decrease in the conduction-band (CB) edge energy with increasing x, whereas the valence-band edge energies were invariant. The evolution in the CB structures was analyzed using the concept of metal-ion crystal fields in the t and m cluster models.