Activation of acceptor levels in Mn implanted Si by pulsed laser annealing

The success of GaMnAs ferromagnetic semiconductors stands on two facts: (1) the efficient suppression of Mn-rich precipitates and (2) the large hole concentration created by substitutional Mn ions. If GaMnAs can be a guide, these two prerequisites should be considered when fabricating Si based ferromagnetic semiconductors. In this paper, nearly intrinsic Si wafers were implanted with Mn ions. The implanted Si films were annealed by pulsed laser annealing (PLA) or rapid thermal annealing (RTA). Activation of acceptors was only realized in the PLA films with a free hole concentration of 4×1017 cm-3, compared to the activation of donors in RTA films with a free electron concentration of 6×1015 cm-3. The PLA films reveal negative magnetoresistance with MR= 0.5% at 20 K and 30 K and at 7 T, hinting towards spin polarization of holes. Ferromagnetism was probed for both RTA and PLA films by a SQUID magnetometer at low temperatures. The formation of ferromagnetic MnSi1.7 nanoparticles has been proven in RTA films by synchrotron radiation X-ray (SR-XRD) measurements [1] and could be excluded in Mn implanted Si annealed by PLA. [1] S. Zhou et al., Phys. Rev. B 75, 085203 (2007).