Study on spin injection and detection in germanium using crystalline ferromagnetic tunnel contacts

Abstract

To maintain the rapid development of electronics, alternative technologies that go beyond downscaling of the devices are required. Spintronics, in which digital data is represented by the electron spin, may provide a solution for future electronics. In particular, semiconductor spintronics, where the unique features of ferromagnet (FMs) and semiconductors (SCs) are combined, raises the possibility to devise a new spin-based information technology. The injection, control, and detection of spin polarization in SC are the main building blocks of SC spintronics. Notably, significant progress has been recently made in establishing the two building blocks of the spin injection and detection, particularly in silicon, the mainstream SC, by developing ferromagnetic tunnel contacts, which provide a reliable and robust means for the efficient spin injection and detection in SC. Triggered by the progress in silicon, germanium has recently received significant attention because of many merits of Ge: a large spin-diffusion length due to the high carrier mobility, the possibility of spin control via non-negligible spin-orbit coupling, the feasibility of epitaxial FM/MgO tunnel contacts to the Ge employing the lattice matching of Ge with MgO, and optical spin pumping through the quasi-direct band gap of Ge. In order to utilize the merits and potential of Ge for SC-spintronic appplication, the experimental demonstration of spin injection and detection in Ge system and systematic investigation of spin phenomena in this system are crucial. This dissertation aims to investigate the issues for the development of Ge spintronics, to experimentally demonstrate the spin injection and detection in Ge by developing suitable ferromagnetic tunnel contacts to the Ge, and to provide viable routes for the realization of Ge-based spintronic devices. We develop the single-crystalline bcc CoFe/MgO(001) tunnel contacts to Ge with the proper resistance-area (RA) product, satisfying the requireme...