Site of Mn in Mn delta-doped GaAs: X-ray absorption spectroscopy

In order to determine the local structure of Mn in delta-doped GaAs layers we have carried out an x-ray absorption spectroscopy experiment at the Mn-K edge in samples grown by molecular beam epitaxy with and without Be co-doping. Mn-Mn atomic correlations have not been found within similar to 5 A radius, ruling out the presence of metallic clusters or local Mn enrichment. In samples deposited at 300 degrees C, Mn substitutionally occupies the Ga site with a local expansion (approximate to 2%) of the first-neighbor distance with respect to GaAs; the second neighbors remain at a distance very close to that of the host lattice, indicating that the structural perturbation induced by Mn is very localized. Ab initio simulation of the x-ray absorption near edge structure spectra confirmed that Mn enters the Ga, rather than the As, site. Samples grown at 450 degrees C exhibit a reduction of the first shell coordination number, suggesting the initial phases of MnAs precipitation. In the case of Be co-doping the downward shift of the Fermi energy leads to the appearance of Mn in tetrahedral interstitial sites, of which we provide a previously unavailable local structural description.