Ferromagnetism of Mn5Ge3 Precipitates in Mn-implanted Self-organized Ge/Si Quantum Dots

One layer of self-assembled Ge quantum dots with Si barrier were grown on high resistivity (100) p-type Si substrates by rapid thermal chemical vapor deposition followed by Mn ion implantation and post-annealing. A presence of ferromagnetic structure was confirmed in the dilute magnetic quantum dots (DMQD). The DMQD through 10 min annealing was found to be homogeneous, and to exhibit p-type conductivity, insulating property, and ferromagnetic ordering with a Curie temperature, Tc=170 K. On the other hand, the DMQD through 30 and 60 min annealing was found to be semi-insulating and ferromagnetic ordering with a Curie temperature over 300 K. The XRD data show that there is a phase separation of Mn rich phases Mn5Ge3 from MnGe nanostructure. Therefore, it is likely that the ferromagnetic exchange coupling of sample with Tc=170 K is hole-mediated and the ferromagnetism in sample with Tc>300 K is due to Mn5Ge3 phase.