Geometrical Anatomy for Oxygen Vacancies in Epitaxial Hf0.5Zr0.5O2 Films Grown via Atomic Layer Deposition

The selective influence of elastic strain on the formation of oxygen deficiencies in (001)-, (110)-, and (111)- epitaxial Hf0.5Zr0.5O2 films grown by using atomic layer deposition is reported. Optical spectroscopy, conducted using UV-vis spectroscopic ellipsometry on these Hf0.5Zr0.5O2 films grown on yttria-stabilized zirconia substrates, revealed a dominant shallow trap level in the (111)-oriented Hf0.5Zr0.5O2 film. X-ray photoemission spectroscopy demonstrated that the strong oxygen deficiency is preferred in the (111)-oriented Hf0.5Zr0.5O2 film. Density functional theory calculations of oxygen vacancy formation energy also showed a pronounced preference for oxygen deficiencies in the (111) orientation. This selective formation of oxygen vacancies in the (111)-oriented Hf0.5Zr0.5O2 film suggests that the latent phenomena associated with oxygen defects in functional Hf0.5Zr0.5O2 films are partly attributed to the directional strain in the (111) orientation.