NON-MAGNETIC SEMICONDUCTOR SPINTRONICS: INNOVATIONS IN NANOSCALE, HIGHLY SPIN-ORBIT COUPLED QUANTUM WELL SYSTEMS

这项提议的目的是提供在所有非磁性半导体系统中注入和检测自旋极化电流的新方法。这一领域是利用自旋-轨道耦合效应控制自旋的领域，是世界各地激烈的理论活动的主题，尽管到目前为止发表的实验工作相对较少。人们感兴趣的一个主要原因是，无论是生产室温磁性半导体还是从磁性金属中注入的挑战都被绕过了。缺乏实验活动的一个重要原因是难以控制半导体材料中的自旋-轨道耦合，这些材料对(光电子)的影响很小。利用最新的自旋相关弹道输运理论，利用窄禁带半导体(NGS)量子阱结构中的高自旋-轨道耦合效应，提出了一种新的方法。这些材料最近被英国工作人员证明能够提供晶体管的终极速度和功耗，现在可以认为这项技术已经成熟。这一提议将利用和加强英国在这一领域的领先地位，并将其转化为新的优势。提出了用于自旋过滤、发射和探测的装置，这将为自旋电子界提供一套至关重要的工具。成功开发基于自旋的新型电子器件需要建立新的实验方法来产生、测量和操纵自旋极化电流。根据国际半导体路线图，为了实现全电子半导体自旋电子器件，必须解决两个挑战之一。要么必须成功地设计铁磁性金属/半导体界面以包括自旋保持隧道势垒，要么必须制造与标准电子工业材料(Si、GaAs和GaN)兼容的室温稀磁半导体。目前的提案描述了一种以新方式利用现有材料和技术的替代解决方案。这个项目将研究纳米结构中的自旋动力学和相关现象，并将获得的物理理解应用于在半导体中创建自旋极化，而不依赖于外部铁磁源的存在。简单地说，我将在缺乏反转对称性的材料和结构中利用运动电子自旋态的非简并性。在大多数目的和大多数材料中，这些自旋分裂是可以忽略不计的。然而，可以利用电子自旋的二色性，例如在具有不同自旋-轨道耦合强度的两种材料之间的界面处的弹道区域中。在这个被称为“自旋光学”的新兴领域，已经证明了自旋相关反射，并提出了一种类似折射(和负折射)的效应。弹道系统还提供了利用回旋运动的自旋相关性质的机会。类似地，自旋分裂可用于用于自旋注入和检测的共振隧道二极管结构中，其中沿生长方向施加的电压可优先允许传输自旋向上或向下的电子。这些机制具有用于半导体自旋电子应用的自旋过滤器的巨大潜力，从而避免了从铁磁性金属或稀磁半导体中注入自旋的需要。

The aim of this proposal is to provide new methods of injecting and detecting spin polarised currents in all non-magnetic semiconductor systems. This area, the control of spins using spin-orbit coupling effects, is the subject of intense theoretical activity around the world, though so far relatively little experimental work has been published. One of the primary reasons for the interest is that the challenges in either producing room-temperature magnetic semiconductors or in injecting from magnetic metals are both by-passed. One important reason for the paucity of experimental activity is the difficultly in controlling spin-orbit coupling in the semiconductor materials of primary importance for (opto-)electronics, where the effects are small. The methods presented here utilise the high spin-orbit coupling in narrow gap semiconductor (NGS) quantum well structures, using the latest theories of spin dependent ballistic transport. These materials have recently been shown by UK workers to be capable of delivering the ultimate in speed and power consumption for transistors, and the technology may now be considered as having reached maturity. This proposal will exploit and strengthen the UK's lead in this area, and turn it to new advantage. Devices for spin filtering, emission and detection are proposed which will provide a crucially important set of tools for the spintronic community.Successful development of novel spin-based electronic devices requires establishing new experimental methods of creating, measuring and manipulating spin-polarised currents. According to the International Semiconductor Roadmap in order to realise an all electrical semiconductor spintronic device one of two challenges must be met. Either successful engineering of the ferromagnetic metal/semiconductor interface has to be achieved to incorporate spin preserving tunnel barriers or the fabrication of room temperature dilute magnetic semiconductors compatible with the standard electronic industry's materials (Si, GaAs and GaN). The current proposal describes an alternative solution that utilises existing materials and technologies in a new way. This project will investigate spin kinetics and related phenomena in nanostructures, and apply the physical understanding gained to the creation of a spin polarisation within the semiconductor without reliance on the presence of an external ferromagnetic source. Simply put, I shall exploit the non-degeneracy of moving electron spin states in materials and structures which lack inversion symmetry. For most purposes and in most materials these spin splittings are negligibly small. However, it is possible to utilise the dichromatic nature of electron spin, for example in the ballistic regime at the interface between two materials of different spin-orbit coupling strength. In this emerging field, dubbed 'spin optics', spin dependent reflection has been demonstrated and a similar refraction (and negative refraction) -like effect has been proposed. The ballistic regime also presents the opportunity to use the spin dependent nature of cyclotron motion. Similarly, the spin splitting may be utilised in resonant tunnel diode structures for spin injection and detection, where a voltage applied along growth direction can preferentially allow transmission of either spin up or down electrons. These mechanisms have great potential for spin filters for semiconductor spintronic applications, which avoid the need for spin injection from ferromagnetic metals or dilute magnetic semiconductors.