NER: Spin Injector for Nanomagnetics and Spintronics Research

摘要本论文是响应纳米尺度科学与工程计划，项目招标NSF 01-157，在ners类别。该提案的重点是开发和表征一类独特的金属半导体异质结构，这可能会导致自旋注入器的生产。具体来说，在表征纳米磁性和自旋电子材料界面的自旋输运和散射性质方面存在问题。当人们考虑各种潜在的杂化结构时，能够探测半导体、铁磁体、非磁性金属和绝缘体之间界面的自旋相关传输特性的需求变得至关重要。我们的目标是制造和表征一种结构，通过提供易于控制的自旋极化电子源，允许人们询问自旋相关的传输特性。该装置使用圆偏振光激发GaAs内的自旋相关载流子，并结合银薄膜量子阱自旋滤波器来选择热电子的能量。这种能量可选择的自旋极化电子源然后形成磁结构后续生长的衬底。我们将利用在该自旋注入器上生长的Co膜的空少数态作为分析仪来表征自旋极化的程度。虽然改变砷化镓的掺杂提供了一个粗略的能量选择，但明智地选择银的厚度提供了通过相关的阿格量子阱态的能量来微调这些电子的能量。我们计划演示、改进和校准该装置，包括在裂解GaAs（110）和GaAs（100）晶圆上生长量子稳定的Ag薄膜。我们已经证明，这些银薄膜表现出量子阱态，它们将被用来进一步过滤自旋极化电子的能量。为了分析这些电子的自旋极化，我们将在Ag/GaAs结构上轴向生长Co，并校准自旋相关的输运到空的少数态带，这既作为GaAs电子极化的函数，也作为Co的磁化的函数。未来的扩展包括纳入anAl2O3绝缘势垒，以测试实际自旋隧穿装置的操作。在整个研究计划中，重点将放在纳米相异质结构的原子/形态和电子特性与随后的自旋相关电导的相关性上。这个项目在几个方面影响了磁学领域。这种结构提供了一种廉价的工具来询问自旋输运性质，并提供了自旋极化光发射和逆光发射的替代方案。一旦校准，它可以用来快速评估先进材料（如半金属薄膜）的自旋相关输运特性。此外，它可以直接用于提供发生在自旋电子结构界面上的自旋相关散射过程的有价值的数据。

AbstractThis proposal was received in response to the Nanoscale Science andEngineering Initiative, Program Solicitation NSF 01-157, in the NERcategory. The proposal focuses on the development and characterization ofone unique class of metal-semiconductor heterostructures, which potentiallywill result in production of a spin injector. Specifically, problems existin characterizing the nature of spin transport and scattering through theinterfaces of nanomagnetic and spintronic materials. As one considersvarious potential hybrid structures, the need to be able to probe thespin-dependent transmission properties of the interfaces betweensemiconductors, ferromagnets, non-magnetic metals, and insulators becomescritical.Our objective is to fabricate and characterize a structure that will allowone to interrogate the spin-dependent transmission properties by providingan easily-controlled source of spin-polarized electrons. The device usescircularly-polarized light to excite spin-dependent carriers within GaAs,and incorporates a Ag thin-film quantum-well spin-filter to energy selectthe hot electrons. This source of energy-selectable spin-polarizedelectrons then forms the substrate for the subsequent growth of magneticstructures. We will characterize the degree of spin-polarization by usingthe empty minority states of a Co film grown on this spin injector as ananalyzer. While changing the doping of the GaAs provides a coarse energyselection, judicious choice of the Ag thickness provides a fine-tuning ofthe energy of these electrons via the energetics of the relevant Agquantum-well state.Our plan to demonstrate, refine, and calibrate this device involves thegrowth of quantum-stabilized Ag films on cleaved GaAs(110) and on GaAs(100)wafers. We have already shown that these Ag films exhibit quantum-wellstates and they will be used to further energy-filter the spin-polarizedelectrons. To analyze the spin-polarization of these electrons, we willepitaxially grow Co on the Ag/GaAs structure and calibrate thespin-dependent transport into the empty minority-state bands, both as afunction of the polarization of the electrons from GaAs as well as themagnetization of the Co. Future extensions include the incorporation of anAl2O3 insulating barrier to test the operation in practical spin-tunnelingdevices. Throughout the research plan, emphasis will be placed oncorrelating atomic/morphological and electronic properties of nanophaseheterostructures with ensuing spin-dependent conductance.This project impacts the field of magnetics in several ways. Thisstructure provides an inexpensive tool to interrogate spin transportproperties and provides an alternative to spin-polarized photoemission andinverse photoemission. Once calibrated, it can be used to quickly evaluatethe spin-dependent transport properties of advanced materials such ashalf-metallic thin-films. Furthermore, it can be used in a direct mannerto provide valuable data on the spin-dependent scattering processes thatoccur at the interfaces of spintronic structures.