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

Self-assembled MnGe quantum dots (QDs) on a Si substrate or GeSi virtual substrate (VS) were grown by molecular beam epitaxy. The GeSi VS of different thicknesses and Ge compositions x were utilized to modulate the ferromagnetic properties of the above QDs. The MnGe QDs on GeSi 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 GeSi 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 GeSi 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.