Negative-U and polaronic behavior of the Zn-O divacancy in ZnO

Article

关键词: ELECTRICAL CHARACTERIZATION;    ULTRASOFT PSEUDOPOTENTIALS;    DEFECTS;    CENTERS;    HYDROGEN;    VACANCY;   

DOI  :  10.1103/PhysRevB.99.174106

来源: SCIE

【 摘 要 】

Hybrid functional calculations reveal the Zn-O divacancy in ZnO, consisting of adjacent Zn and O vacancies, as an electrically active defect exhibiting charge states ranging from 2+ to 2- within the band gap. Notably, the divacancy retains key features of the monovacancies, namely, the negative-U behavior of the O vacancy and the polaronic nature of the Zn vacancy. The thermodynamic charge-state transition levels associated with the negative-U behavior epsilon(0/2-), epsilon(-/2-), and epsilon(0/-) are predicted to occur at 0.22, 0.42, and 0.02 eV below the conduction band minimum, respectively, resulting in U = -0.40 eV. These transition levels are moved closer to the conduction band, and the magnitude of U is lowered compared to the values for the O vacancy. Further, the interaction with hydrogen is explored, and it is shown that the divacancy can accommodate up to three H atoms. The first two H atoms prefer to terminate O dangling bonds at the Zn vacancy, while the geometrical location of the third depends on the Fermi level position. The calculated electrical properties of the divacancy are in excellent agreement with those reported for the E4 center observed by deep-level transient spectroscopy, challenging the O vacancy as a candidate for this level.

【 授权许可】

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