Carrier effects on ferromagnetism of MnxGe1-x quantum dots

Mn-doped Ge quantum dots (QDs) were grown on Si (001) substrates by molecular beam epitaxy. At the same time, modulation doping of boron (B) with different concentrations at 10 nm beneath the QD layers is utilized to modulate the concentration of holes in the QDs. For Mn uni-doped and B uni-modulation-doped Ge QD samples, no credible ferromagnetic signals in the hysteresis loop were observed, while a significant ferromagnetic signal was observed for the Mn-doped Ge QD samples with a high modulation doping of B. Both the magnetic moment and the Curie temperature of the Mn-doped Ge QD samples increase with the modulation doping concentration of B. The increase in the Curie temperature is believed to associate with the exotic holes in the QDs from B dopants, which enhanced coupling between the holes and the localized Mn dopants in the QDs. Those results show a way to enhance the ferromagnetic properties of Mn-doped Ge QDs and provide more evidence to the carrier-mediated ferromagnetism model. Published by AIP Publishing.