Magnetic and transport properties of Mn-implanted Ge/Si quantum dots

Twenty layers 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 (Si0.45Ge0.55)Mn0.05 diluted magnetic quantum dots by magnetometry using a superconducting quantum interference device. The (Si0.45Ge0.55)Mn0.05 material was found to be homogeneous, and to exhibit p-type conductivity and ferromagnetic ordering with a Curie temperature, T C = 160 K . Temperature-dependent electrical resistivity in (Si0.45Ge0.55)Mn0.05 material indicates that manganese introduces two acceptor levels in germanium at 0.14 eV from the valence band and 0.41 eV from the conduction band implying Mn substituting Ge. Therefore, it is likely that the ferromagnetism observed in Mn-implanted GeSi quantum dots is hole-mediated ferromagnetism.