Microscopic investigation of the structural and electronic properties of ion implanted Mn-Ge alloys

We review recent results of an extensive experimental study of ion implanted Mn-Ge(100) alloys fabricated by systematically varying the Mn dose (in the range 1-4 x 10(16) at/cm(2)) and the Ge substrate temperature (from room temperature up to 300 degrees C) during the implantation. The samples have been investigated by means of X-ray photoemission spectroscopy, scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, and scanning tunneling microscopy and spectroscopy. The combined investigation allows to determine, with an unprecedented deal of information at the nanometer scale, the morphological, structural, and electronic properties of such alloys. We evidence a porous to continuous transition in the surface morphology of the implanted layer when passing from 190 to 240 degrees C implantation substrate temperature. At higher implantation temperatures we directly demonstrate Mn dilution in the Ge matrix and also show the presence of extrinsic phases like Mn rich clusters. The presence of Mn rich precipitates is directly evidenced with transmission electron microscopy and corresponding energy loss Mn elemental maps taken at the Mn L, edge. Larger clusters (with diameter greater that 10 nm) are in the Mn,Ge, phase and are metallic, as demonstrated with scanning tunneling spectroscopy. Smaller clusters are still Mn rich but typically in an amorphous phase. These clusters are semiconducting with 0.45 eV energy gap. The results on the local electronic structure of the alloys investigated with scanning tunneling spectroscopy are also discussed in comparison with ab-initio calculations.