Ferromagnetism in Mn-Implanted Epitaxially Grown Ge on Si(100)

F ERROMAGNETISM IN M N -I MPLANTED E PITAXIALLY G ROWN G E ON S I (100) S. Guchhait 1 , M. Jamil 1 , H. Ohldag 2 , A. Mehta 2 , E. Arenholz 3 , G. Lian 4 , A. LiFatou 4 , D. A. Ferrer 1 , J. T. Markert 5 , L. Colombo 4 and S. K. Banerjee 1† Microelectronics Research Center, The University of Texas at Austin, Austin, TX Stanford Synchrotron Radiation Lightsource, Menlo Park, CA Advanced Light Source, Berkeley, CA Texas Instruments Incorporated, Dallas, TX Department of Physics, The University of Texas at Austin, Austin, TX A BSTRACT We have studied ferromagnetism of Mn-implanted epitaxial Ge films on silicon. The Ge films were grown by ultra high vacuum chemical vapor deposition using a mixture of germane (GeH 4 ) and methylgermane (CH 3 GeH 3 ) gases with a carbon concentration less than 1at%, and observed surface rms roughness of about 0.5 nm, as measured by atomic force microscopy. Manganese ions were implanted in epitaxial Ge films grown on Si (100) wafers to an effective concentration of about 16at%, 12at%, 6at% and 2at%. SQUID measurements showed that only the three highest Mn concentration samples are ferromagnetic, while the fourth sample, with [Mn]=2at%, is paramagnetic. X-ray absorption spectroscopy (XAS) and X-ray Magnetic Circular Dichroism (XMCD) measurements indicate that localized Mn moments are ferromagnetically coupled below the Curie temperature. Isothermal annealing of Mn- implanted Ge films with [Mn]=16at% at 300 o C for up to 1200 seconds decreases the magnetization but does not change the Curie temperature, suggesting that the amount of the magnetic phase slowly decreases with time at this anneal temperature. Furthermore, transmission electron microscopy (TEM) and synchrotron grazing incidence x-ray diffraction (GI-XRD) experiments show that the Mn-implanted region is amorphous, and we believe that it is this phase that is responsible for the ferromagnetism. This is supported by our observation that high temperature annealing leads to recrystallization and transformation of the material into a paramagnetic phase. samaresh@physics.utexas.edu banerjee@ece.utexas.edu