Origin of three-terminal Hanle-type signals in low-temperature ferromagnet-silicon structures with direct Schottky contacts

We analyze three-terminal electrical Hanle-type measurements in CoFe/Si devices. We show that at low temperatures there exists a Lorentzian-like dependence of the voltage signal on external magnetic field that does not correspond to the spin lifetime. The signal stems from spin-dependent scattering of electrons by neutral impurities in the bulk Si channel. The measured signal amplitude is explained by exchange interactions between free (injected) and localized electrons, while the ``Lorentzian" width by exchange between localized electrons on adjacent impurities. The theory reproduces the observed dependencies on temperature and injected current density.