  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.
