Spin Polarization by Current

Abstract

A simple prototype of a semiconductor spin transport device consists of a lateral semiconductor channel with two ferromagnetic contacts, one of which serves as a source of spin-polarized electrons and the other as a detector. I will discuss recent results of optical and electrical studies of spin transport in ferromagnet-semiconductor structures consisting of Fe Schottky tunnel barrier contacts on an n-doped GaAs channel. In the first set of experiments, we have used optical Kerr microscopy to image spin-polarized carriers that are injected into the channel [1]. Second, we have shown that spin-polarized carriers that accumulate at a forward-biased Fe/GaAs Schottky barrier can be detected electrically [2]. Our most recent experiments have demonstrated that spin-polarized carriers injected at the source contact can be detected electrically [3]. For these measurements, we have employed a non-local ferromagnetic detection contact at which the spin-dependent electrochemical potential is sensitive to the relative magnetizations of the source and detector. A transverse magnetic field suppresses the non-local signal by inducing spin precession and dephasing in the GaAs channel (the Hanle effect). A simple drift-diffusion model that incorporates precession provides a quantitative description of the data. The sign of the signal varies with the injection current and is correlated with the spin polarization in the GaAs channel measured optically. These results therefore demonstrate a fully electrical scheme for spin injection, transport, and detection in a lateral semiconductor device. This work was carried out in collaboration with Xiaohua Lou, Scott Crooker, Christoph Adelmann, Madalina Furis, Darryl Smith, Eric Garlid, Jianjie Zhang, Soren Flexner, Madhukar Reddy, and Chris Palmstrom. We are grateful for the support of the Office of Naval Research, the National Science Foundation MRSEC, IGERT, and NNIN Programs, and the Los Alamos National Laboratory LDRD Program.