GeSi virtual-layer enhanced ferromagnetism in self-assembled MnGe quantum dots grown on Si wafers by molecular beam epitaxy

Self-assembled Mn 0.06 Ge 0.94 quantum dots (QDs) on a Si substrate or Ge x Si 1− x virtual substrate (VS) were grown by molecular beam epitaxy. The Ge x Si 1− x VS of different thicknesses and Ge compositions x were utilized to modulate the ferromagnetic properties of the above QDs. The MnGe QDs on Ge x Si 1− x VS show a significantly enhanced ferromagnetism with a Curie temperature above 220 K. On the basis of the microstructural and magnetization results, the ferromagnetic properties of the QDs on Ge x Si 1− x VS are believed to come from the intrinsic MnGe ferromagnetic phase rather than any intermetallic ferromagnetic compounds of Mn and Ge. At the same time, we found that by increasing the Ge composition x of Ge x Si 1− x VS, the ferromagnetism of QDs grown on VS will markedly increase due to the improvements of hole concentration and Ge composition inside the QDs. These results are fundamentally important in the understanding and especially in the realization of high Curie temperature MnGe diluted magnetic semiconductors. The ferromagnetism of MnGe QDs grown on GeSi VS will markedly increase by increasing the Ge composition of GeSi VS.