Phase-separated high-temperature-annealed (Ga,Mn)As: A negative charge-transfer-energy material

TL;DR

This study investigates phase-separated (Ga,Mn)As with MnAs nanoclusters, revealing its placement in the negative charge-transfer-energy class and analyzing how strain and cluster size influence its metal-insulator transition.

Contribution

It identifies the electronic classification of phase-separated (Ga,Mn)As as a negative charge-transfer-energy material and explores how strain and cluster size affect its electronic phase transitions.

Findings

(Ga,Mn)As belongs to negative charge-transfer-energy class

Strain influences the metal-insulator transition

Cluster size affects the opening of a covalent gap

Abstract

The approximate location in the Zaanen-Sawatzky-Allen diagram of the phase-separated (Ga,Mn)As material, consisting of MnAs nanoclusters embedded in GaAs, is determined on the basis of configuration-interaction (CI) cluster-model analysis of their Mn 2p core-level photoemission. The composite material is found to belong to the special class of materials with negative charge-transfer energy (delta). As such, its metallic or insulating/semiconducting behavior depends on the strength of the p-d hybridization (affected by strain) relative to the (size-dependent) p-bandwidth. Whereas internal strain in the embedded clusters counteracts gap opening, a metal-to-semiconductor transition is expected to occur for decreasing cluster size, associated to the opening of a small gap of p-p type (covalent gap). The electronic properties of homogeneous and phase-separated (Ga,Mn)As materials are analyzed, with emphasis on the nature of their metal-insulator transitions.