Valency Configuration of Transition Metal Impurities in ZnO

TL;DR

This study uses advanced computational methods to determine the valency states of transition metal impurities in ZnO, revealing their charge states depend on doping conditions and the impurity's electronic configuration.

Contribution

It provides a detailed theoretical analysis of TM impurity charge states in ZnO using self-interaction corrected calculations, highlighting the influence of doping on valency configurations.

Findings

TM impurities favor a 2+ valency in pure ZnO.

The donor level is located in the ZnO gap.

Charge states depend on n- or p-type doping conditions.

Abstract

We use the self-interaction corrected local spin-density approximation to investigate the ground state valency configuration of transition metal (TM = Mn, Co) impurities in n- and p-type ZnO. We find that in pure Zn1-xTMxO, the localized TM2+ configuration is energetically favored over the itinerant d-electron configuration of the local spin density (LSD) picture. Our calculations indicate furthermore that the (+/0) donor level is situated in the ZnO gap. Consequently, for n-type conditions, with the Fermi energy eF close to the conduction band minimum, TM remains in the 2+ charge state, while for p-type conditions, with eF close to the valence band maximum, the 3+ charge state is energetically preferred. In the latter scenario, modeled here by co-doping with N, the additional delocalized d-electron charge transfers into the entire states at the top of the valence band, and hole carriers will only exist, if the N concentration exceeds the TM impurity concentration.