Electrical spin injection in silicon and the role of defects

Three-terminal devices, where the same ferromagnetic electrode is used for electrical spin injection and detection, is a very easy and powerful tool to probe the spin properties in nonmagnetic materials. For instance, it has been intensively used to study spin injection and detection in silicon. However the interpretation of the magnetoresistance signals observed experimentally is still under debate. In particular, a controversy has been raised about the experimental spin signal which is orders of magnitude larger than the predicted value. Recently, Song et al. [Phys. Rev. Lett. 113, 047205 (2014)PRLTAO0031-900710.1103/PhysRevLett.113.047205] proposed that the magnetoresistance signal measured using the Hanle effect in a three-terminal geometry is due to defects or impurities in the tunnel barrier separating the ferromagnetic electrode from the silicon channel. It has also been supported by the experimental work of Txoperena et al. [Phys. Rev. Lett. 113, 146601 (2014)PRLTAO0031-900710.1103/PhysRevLett.113.146601]. In this study, we perform electrical spin injection/detection measurements using three-terminal devices in different silicon films and study the role of defects. For this purpose, we use the tunneling inelastic spectroscopy to measure the Hanle effect and control the presence of defects in the tunnel barrier. Contrary to previous reports, we demonstrate that defects have no significant contribution to the spin signal. From a comparison with capacitance-voltage measurements in n-doped germanium in which interface states contribute to the spin signal, we also conclude on the presence of interface states in silicon.