Phase stability and optical properties of Y-doped HfO₂ from first principles

Hafnia (HfO₂), as a high-k material in its tetragonal and cubic phases, has long been recognized as valuable in complementary metal-oxide-semiconductor applications. The discovery of ferroelectricity in HfO₂ thin films, with a Pbc21 orthorhombic phase, has been the subject of much recent theoretical and experimental research. One path to stabilizing the ferroelectric phase is through the incorporation of various dopants. Here, we use first-principles methods to explore how Y doping, both with and without associated oxygen vacancies, affects the stability of various candidate HfO₂ structures. In addition, we investigate the effects of the dopants and vacancies on the electronic structure and optical properties, which are key to making connections with experimental results and are highly relevant to the possible incorporation of ferroelectric HfO₂ into a variety of devices.