Electronic structure of transition metal impurities in p-type ZnO

TL;DR

This study uses advanced computational methods to explore how transition metal impurities behave in p-type ZnO, revealing their valency states, donor levels, and conditions for ferromagnetism.

Contribution

It provides new insights into the electronic structure and magnetic properties of TM-doped ZnO, especially regarding the effects of co-doping with nitrogen.

Findings

TM impurities favor a +2 valency in ZnO without additional holes.

The (+/0) donor level is in the band gap, influencing valency.

Carrier-mediated ferromagnetism is possible with sufficient N doping.

Abstract

The self-interaction corrected local spin-density approximation is used to investigate the ground-state valency configuration of transition metal (TM=Mn, Co) impurities in p-type ZnO. Based on the total energy considerations, we find a stable localised TM$^{2+}$ configuration for a TM impurity in ZnO if no additional hole donors are present. Our calculations indicate that the (+/0) donor level is situated in the band gap, as a consequence of which the TM$^{3+}$ becomes more favourable in p-type ZnO, where the Fermi level is positioned at the top of the valence band. When co-doping with N, it emerges that the carrier-mediated ferromagnetism can be realized in the scenario where the N concentration exceeds the TM impurity concentration. If TM and N concentrations are equal, the shallow acceptor levels introduced by N are fully compensated by delocalised TM d-electrons.