(Ge,Mn): A ferromagnetic semiconductor for spin injection in silicon
by M. Jamet, T. Devillers, I-S. Yu, A. Barski, P. Bayle-Guillemaud, J. Rothman, V. Favre-Nicolin, S. Tardif, S. Cherifi, J. Cibert, L. Grenet, P. Noe, V. Calvo, P. Warin, J-M. Hartmann, B. Rodmacq, S. Auffret, Y. Samson
International Journal of Nanotechnology (IJNT), Vol. 7, No. 4/5/6/7/8, 2010

Abstract: Spin injection in semiconductors has been a long-standing issue in the field of spintronics for nearly 10 years. Only at the end of the 1990s, electrical spin injection in III-V semiconductors could be demonstrated using spin-light emitting diodes as spin detectors. Although silicon is the key material of microelectronics, spin injection in silicon could be achieved only recently in 2007. For this purpose, we have developed a new ferromagnetic semiconductor (Ge,Mn) that may be suitable for spin injection in silicon. Indeed this material is compatible with mainstream silicon technology and is predicted as a half-metallic ferromagnet. We have used low temperature molecular beam epitaxy to grow germanium films doped with manganese. Growth temperatures as well as Mn concentrations were kept low in order to avoid phase separation due to the low solubility of Mn in Ge. Careful structural and chemical analyses showed that (Ge,Mn) films are not diluted magnetic semiconductors. We rather observe high-T_C ferromagnetic self-assembled nanocolumns in the germanium film with magnetic properties strongly dependent on growth parameters. We could clearly identify four different magnetic phases in Ge_1−xMn_x films: diluted paramagnetic Mn atoms in the germanium matrix, low T_C (<200 K) nanocolumns, high T_C nanocolumns (>400 K) and Ge₃Mn₅ clusters. The relative weight of each phase mainly depends on the growth temperature and to a lesser extent to Mn concentration. In parallel, we have developed methods to detect spin injection in silicon. Using a ferromagnetic metal with perpendicular magnetisation we could perform spin injection in silicon in the tunnelling regime through an alumina barrier. Spin detection was optically achieved using a SiGe/Si spin-light emitting diode without applying a magnetic field.

Online publication date: Sun, 21-Feb-2010

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