Spintronic device physics in Si/Ge Heterostructures.

世界各地的物理学家正在对半导体中的自旋注入和输运进行密切的研究，他们受到对凝聚态物质的迷人新见解的推动，意识到新设备和后续技术的巨大潜力。然而，自旋注入及其检测带来了特殊的挑战。很多注意力都集中在技术上重要的材料上：GaAs，它的光学特性有助于自旋检测，最近又因为Si的长自旋寿命而备受关注。在这里，我们提出了一种基于锗的新方法。Ge与Si工艺兼容，具有比GaAs更长的自旋寿命，比GaAs或Si具有更高的室温空穴迁移率，并且由于其更高的自旋-轨道耦合而比Si具有更好的调制性能。由于载流子迁移率的显著增强，SiGe异质结技术还具有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RT自旋通过Ge的输运和提取，该结构由在GaAs上外延生长的Ge和电沉积的Ni/Ge肖特基接触组成[C.Shenet al.，Appl.太棒了。让我们来吧。97、162104(2010年)]。在这里，我们建议在这项工作的基础上，通过增量掺杂和能带结构工程来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沟道中的相干传输，从而充分利用Si-Ge系统。这个项目的最终结果应该是令人兴奋的在室温下运行的两端半导体自旋阀的前景，以及在这种设备中通过栅电极进行自旋调制的早期演示。该计划将结合合作伙伴的互补专业知识：Warwick在SiGe外延和载流子传输方面，南安普顿在肖特基势垒研究方面，剑桥在半导体自旋传输方面通过光学和电气手段，以及南安普顿纳米制造中心的设施和东芝欧洲研究有限公司的工业支持。

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.