Localization of the dopant in Ge:Mn diluted magnetic semiconductors by x-ray absorption at the Mn K edge.

A unitary picture of the structural properties of Mn(x)Ge(1-x) diluted alloys fabricated by either ion implantation or molecular beam epitaxy (MBE), at various growth temperatures (from 80 to about 623 K) and few per cent concentrations, is proposed. Analysis is based on synchrotron radiation x-ray absorption spectroscopy at the Mn K edge. When the growth temperature exceeds 330 K, the MBE samples show a high number of precipitated ferromagnetic nanoparticles, mainly Mn(5)Ge(3), nucleated from the previous occupation of interstitial tetrahedral sites. Efficient substitution is observed in the case of MBE samples made by alternate layers of GeMn alloys grown at T ≤ 433 K and undoped Ge thick layers. Similar good dilution properties are obtained by implanting Mn ions at low temperatures (80 K). Possible precursors to preferential mechanisms in the alloy formation are discussed on the basis of the present comparative study.