Polaronic hole localization and multiple hole binding of acceptors in oxide wide-gap semiconductors

TL;DR

This paper develops a new theoretical approach to accurately describe hole localization in oxide semiconductors, revealing that certain acceptors can bind multiple holes, which was previously misrepresented by standard methods.

Contribution

It introduces a generalized Koopmans condition to correct localization biases in density functional calculations, enabling accurate prediction of hole localization and multiple hole binding.

Findings

Corrects the bias in standard DFT methods for hole localization

Reveals acceptors in ZnO, In2O3, and SnO2 can bind multiple holes

Provides a more accurate theoretical framework for oxide semiconductors

Abstract

Acceptor-bound holes in oxides often localize asymmetrically at one out of several equivalent oxygen ligands. Whereas Hartree-Fock (HF) theory overly favors such symmetry-broken polaronic hole-localization in oxides, standard local density (LD) calculations suffer from spurious delocalization among several oxygen sites. These opposite biases originate from the opposite curvatures of the energy as a function of the fractional occupation number n, i.e., d2E/dn2 < 0 in HF and d2E/dn2 > 0 in LD. We recover the correct linear behavior, d2E/dn2 = 0, that removes the (de)localization bias by formulating a generalized Koopmans condition. The correct description of oxygen hole-localization reveals that the cation-site nominal single-acceptors in ZnO, In2O3, and SnO2 can bind multiple holes.