Origin of Indium Diffusion in High‑k Oxide HfO₂

Indium (In) out-diffusion through high-k oxides severely undermines the thermal reliability of the next generation device of III-V/high-k based metal oxide semiconductor (MOS). To date, the microscopic mechanism of In diffusion is not yet fully understood. Here, we utilize angle resolved X-ray photoelectron spectroscopy (ARXPS) and density functional theory (DFT) to explore In diffusion in high-k oxide HfO₂. Our ARXPS results confirm the In diffusion through as-prepared and annealed HfO₂ grown on InP substrate. The theoretical results show that the In diffusion barrier is reduced to ∼0.88 eV in the presence of oxygen vacancies (V_O), whereas this barrier is as high as ∼4.78 eV in pristine HfO₂. Fundamentally, we found that the high feasibility of In diffusion is owing to In nonbonding with its neighboring atoms. These findings can be extended to understand the In diffusion in other materials in addition to HfO₂.