Electronic Structure of Oxygen Deficient Noncentrosymmetric Orthorhombic Hf_0.5Zr_0.5O₂

The electronic structure of oxygen vacancies in noncentrosymmetric orthorhombic Hf_0.5Zr_0.5O₂ was investigated with quantum chemical density functional theory simulations. The oxygen vacancies with different coordination in five charged states were investigated. The single electron levels of charged states is located in the band gap, as well as the values of trap thermal and optical ionization energies, indicate that any type of oxygen vacancies can capture both electrons and holes, i.e. they can act as an amphoteric localization center (trap) for charge carriers. The vacancy levels position in the band gap for an added electron is in excellent agreement with the experimental trap thermal ionization energy 1.25 eV for the amorphous Hf_0.5Zr_0.5O₂ film. X-ray photoelectron spectroscopy revealed that high oxygen vacancies concentration generation by the Ar⁺ etching method is not appropriate for o-Hf_0.5Zr_0.5O₂.