Structural Polymorphism Kinetics Promoted by Charged Oxygen Vacancies in HfO_{2}.

Area of Science:

• Materials Science
• Solid State Physics
• Computational Materials Science

Background:

• Oxygen vacancies are critical defects in ferroelectric hafnium oxide (HfO_{2}) devices.
• Atomistic mechanisms for phenomena like wake-up and fluid imprint are not fully understood.

Purpose of the Study:

• To investigate the influence of oxygen vacancy charge states on HfO_{2} polymorph phase transitions.
• To elucidate the kinetic pathways governing ferroelectricity in HfO_{2}-based materials.

Main Methods:

• First-principles calculations combined with variable-cell nudged elastic band technique.
• Application of a lattice-mode-matching criterion for studying phase transitions.
• Systematic analysis of neutral and positively charged oxygen vacancies.

Main Results:

• Positively charged oxygen vacancies kinetically facilitate transitions from nonpolar to polar phases.
• A transient high-energy tetragonal phase plays a key role in these transitions.
• The polar Pca2_{1} phase exhibits extreme charge-carrier-inert ferroelectricity.

Conclusions:

• The charge state of oxygen vacancies intricately couples with structural polymorphism kinetics.
• This coupling is crucial for understanding ferroelectricity, wake-up, fluid imprint, and inertial switching in HfO_{2} thin films.