Mn doped Ge (Ge:Mn) is a promising candidate for a ferromagnetic semiconductor compatible with silicon technology, since Mn acts as a magnetic ion as well as a double acceptor in Ge. Whereas ferromagnetism has been evidenced by magnetization measurements in Ge:Mn, the transport behavior is entirely different from the GaAs:Mn system [1], the prototype of a ferromagnetic semiconductor.

We have prepared a series of Ge:Mn layer by Mn ion implantation into near-intrinsic Ge substrates, at 350 °C (resulting in Mn₅Ge₃ clusters) and -40 °C (without precipitates) [1-4]. The Mn concentration ranges from 0.004% to 10%. For samples with 10% Mn, flash lamp and pulsed laser annealing (PLA) has been applied. We obtained three kinds of samples: (1) very dilute Ge:Mn where no ferromagnetic coupling can be expected [1]; (2) nanocrystalline Mn₅Ge₃ embedded inside the Ge matrix [2]; and (3) diluted Ge:Mn together with Mn-rich spinodal phases [3]. Indeed all samples show p-type conductivity with a hole concentration ranging from 10¹⁸ to 10²⁰ cm^-3. The highest concentrations above 10²⁰ cm^-3 can only be achieved by PLA. In the sample with the largest hole concentration of 2.1×10²⁰ cm^-3, we observed a one-to-one correspondence between the hysteresis in magnetization, magnetoresistance and Hall resistance below 10 K [3, 4]. We argue that the hole concentration is the critical parameter to establish carrier mediated ferromagnetism in Ge:Mn [4]. In addition to the compatibility to Si technology, ion implantation followed by PLA is an established scalable chip technology and may have a significant industry impact.

[1] S. Zhou et al., APL, 95, 172103 (2009).

[2] S. Zhou et al., APL, 95, 192505 (2009).

[3] S. Zhou et al., PRB 81, 165204 (2010).

[4] S. Zhou et al., APL, in press (2010).

Shengqiang Zhou, Institute of Ion Beam Physics and Materials Research, Forschungszentrum Rossendorf, P.O. Box 510119, 01314 Dresden, Germany and State Key Laboratory of Nuclear Physics & Technology, School of Physics, Peking University, Beijing 100871, China, 
Danilo Buerger, Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, Germany
Wolfgang Skorupa*, Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, Germany
Carsten Timm, Institute for Theoretical Physics, Technical University Dresden, Germany
Peter Oesterlin, INNOVAVENT GmbH, Germany
Manfred Helm, Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, Germany
Heidemarie Schmidt, Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, Germany

*presenting author