Spintronic device physics in Si/Ge Heterostructures.

半导体中的自旋注入和输运正受到世界各地物理学家的密切研究，其动机是对凝聚态物质的迷人新见解，意识到新器件和后续技术的巨大潜力。然而，自旋注入及其检测提出了特殊的挑战。许多焦点都集中在技术上重要的材料：GaAs，其中光学特性有助于自旋检测，最近Si的自旋寿命长。在这里，我们提出了一种基于锗的新方法。Ge与Si技术兼容，具有比GaAs更长的自旋寿命，比GaAs或Si更高的室温空穴迁移率，以及由于其更高的自旋-轨道耦合而比Si更好的调制特性。SiGe异质结构技术还具有通过显著增强载流子迁移率来增加自旋扩散长度的潜力。我们最近进行了光学实验，首次证明了通过Ge的RT自旋输运和提取，该实验基于由在GaAs上外延生长的Ge和电沉积的Ni/Ge肖特基接触组成的结构[C. Shen等人，应用物理信函97，162104（2010）]。在这里，我们建议建立在这项工作的基础上，并充分利用硅锗系统，通过δ掺杂和能带结构工程，以最大限度地提高电接触的自旋透明度，并使用应变和低维来增强通道中的相干传输。该项目的高潮应该是在室温下操作的难以捉摸的双端半导体自旋阀的令人兴奋的前景，以及在这种器件中通过栅电极进行自旋调制的早期演示。该方案将联合收割机结合合作伙伴的互补专长：沃里克在硅锗外延和载流子传输方面，南安普顿在肖特基势垒研究方面，和剑桥在半导体自旋输运的光学和电气手段，连同设施的南安普顿纳米纤维中心和工业支持东芝欧洲研究有限公司。

Spin injection and transport in semiconductors is under intense investigation by physicists around the world, motivated by fascinating new insights into condensed matter, aware of considerable potential for novel devices and ensuing technologies. However, spin injection and its detection pose exceptional challenges. Much focus has been on technologically important materials: GaAs, where optical properties aid spin detection, and more recently Si for its long spin lifetimes. Here, we propose a new approach based on germanium. Ge is compatible with Si technology, has a longer spin life time than GaAs, a higher room temperature hole mobility than GaAs or Si, and better modulation properties than Si due to its higher spin-orbit coupling. SiGe heterostructure technology also has the potential to increase spin diffusion lengths by virtue of dramatic enhancements in carrier mobility.We recently carried out optical experiments that demonstrated RT spin transport and extraction through Ge for the first time, based on a structure consisting of Ge grown epitaxially on GaAs and an electrodeposited Ni/Ge Schottky contact [C. Shen et al., Appl. Phys. Lett. 97, 162104 (2010)]. Here, we propose to build upon that work and use the Si-Ge system to its full extent, through delta doping and bandstructure-engineering to maximize spin transparency of the electrical contacts and using strain and low dimensionality to enhance coherent transport in the channel. The culmination of this project should be the exciting prospect of the elusive two-terminal semiconductor spin valve operating at room temperature and an early demonstration of spin modulation by a gate electrode in such a device.The programme will combine the complementary expertise of the partners: Warwick in SiGe epitaxy and in carrier transport, Southampton in Schottky barrier research, and Cambridge in semiconductor spin transport by optical and electrical means, together with the facilities of the Southampton Nanofabrication Centre and industrial support from Toshiba Europe Research Ltd.