Electrical spin injection in p-type Si using Fe/MgO contacts

We report the successful electrical creation of spin polarization in p-type Si at room temperature by using an epitaxial MgO(001) tunnel barrier and Fe(001) electrode. Reflection high-energy electron diffraction observations revealed that epitaxial Fe/MgO(001) tunnel contacts can be grown on a (2 x 1) reconstructed Si surface whereas tunnel contacts grown on the (1 x 1) Si surface were polycrystalline. Transmission electron microscopy images showed a more flat interface for the epitaxial Fe/MgO/Si compared to that of the polycrystalline structure. For the Fe/MgO/p-Si devices, the Hanle and inverted Hanle effects were clearly observed at 300 K by using a three-terminal configuration, proving that spin polarization can be induced in the Si at room temperature. Effective spin lifetimes deduced from the width of the Hanle curve were 95 +/- 6 ps and 143 +/- 10 ps for the samples with polycrystalline and epitaxial MgO tunnel contacts, respectively. The observed difference can be qualitatively explained by the local magnetic field induced by the larger roughness of the interface of the polycrystalline sample. The sample with epitaxial Fe/MgO tunnel contact showed higher magnitude of the spin accumulation with a nearly symmetric behavior with respect to the bias polarity whereas that of the polycrystalline MgO sample exhibited a quite asymmetric evolution. This might be attributed to the higher degree of spin polarization of the epitaxial Fe/MgO(001) tunnel contact, which acts as a spin filter. Our experimental results suggest that an epitaxial MgO barrier is beneficial for creating spins in Si.
Comment: Paper presented at SPIE Nanoscience + Engineering, Spintronics V session in San Diego, US on August 13th, 2012