Ferromagnetism in Mn doped Ge thin films

Exploring ferromagnetism in Group IV semiconductors is of great interest due to their potential application to spintronics. In this presentation, we discuss the ferromagnetism induced in thin Ge films by Mn$^{+}$ ion implantation as well as the correlation between their magnetism and their transport properties. The as-received Germanium on insulator (GOI) wafer consists of 200nm of (100) oriented Ge on 400nm of oxide both on a Si wafer. Mn ions were implanted at 300 $^{o}$C into the Ge layer at 200 KeV. The ferromagnetism has been observed in Ge with a range of Mn concentration from 0.5 to 2 atom {\%}. The sample with 2 {\%} Mn doping has a Curie temperature near 300K and has a moment of $\sim $ 0.7 $\mu _{B}$/Mn at 10 K. Transmission electron microscopy (TEM) reveals the formation of second phase clusters of which are probably responsible for the majority of the magnetism in this sample. In contrast, the 0.5 {\%} and 1 {\%} Mn as implanted Ge thin films behave like diluted ferromagnetic semiconductors, both have Curie temperatures is around 100 $\sim $150 K and the 0.5{\%} sample doesn't show TEM evidence of a second phase. Our data indicates that the transport properties of Mn doped Ge correlates with the magnetism.