Modeling the polaronic nature of p-type defects in Cu_2O: The failureof GGA and GGA+U

摘要

The exact nature of the hole traps reported deep in the band gap of Cu_2Ohas been a topic ofvigorous debate, with copper vacancies and oxygen interstitials both having been proposed as therelevant defects. In this article, the electronic structure of acceptor-forming defects in Cu_2O, namely,copper vacancies and oxygen interstitials, is investigated using generalized gradient approximation(GGA) and GGA corrected for on-site Coulombic interactions (GGA+ U). GGA produces notionallysemimetallic defect complexes, which is not consistent with the experimentally known polaronicnature of conduction in Cu_2O. GGA+Ualso predicts a semimetallic defect complex for the"simple" copper vacancy but predicts the "split" vacancy and both oxygen interstitials arecharacterized by localized polarons, with distinct single particle levels found in the band gap. Forboth methods, however, the positions of calculated transition levels are inconsistent withexperimental ionization levels. Hence neither GGA nor GGA+ U are successful in modeling p-typedefects in Cu_2O.