Spin-Dependent Transport in Metal/Semiconductor Tunnel Junctions
Spin-Dependent Transport in Metal/Semiconductor Tunnel Junctions
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金属/半导体隧道结中的自旋相关输运
DOI：
10.1088/0953-8984/7/49/010
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发表时间：
1995
期刊：
影响因子：
--
通讯作者：
J. Boeck
中科院分区：
文献类型：
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作者：
M. Prins;H. Kempen;H. Leuken;D. Groot;W. Roy;J. Boeck
本文介绍了利用光学自旋取向进行自旋极化隧穿的模型和实验。这涉及到磁性材料和砷化镓（GaAs）之间的隧道结，其中后者被圆偏振光光激发以产生自旋极化载流子。提出了一种考虑半导体表面态载流子捕获的输运模型，并用自旋相关的能量分布函数描述半导体表面。所谓的表面自旋分裂可以从半导体亚表面区极化电子和空穴流动的平衡、磁性材料与半导体表面之间穿过隧道势垒的极化隧穿电流以及半导体表面的自旋弛豫来计算。测量了Co/Al2O3/GaAs薄膜隧道结中圆极化相关的光电流（所谓的螺旋不对称）。在没有隧道势垒的情况下，螺旋度不对称是由磁光效应（磁圆二色性）引起的。在存在隧道势垒的情况下，数据不能仅用磁光效应来解释；这些偏差为自旋极化隧穿现象的发生提供了证据。在Co/ tau -MnAl/AlAs/GaAs结中，没有观察到磁光效应的偏差，这很可能是由于tau -MnAl沿隧穿方向的自旋极化较弱；后者得到了能带结构计算的证实。最后讨论了光激发砷化镓在扫描隧穿显微镜中自旋极化隧穿中的应用。
This paper describes a model as well as experiments on spin-polarized tunnelling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide (GaAs), where the latter is optically excited with circularly polarized light in order to generate spin-polarized carriers. A transport model is presented that takes account of carrier capture in the semiconductor surface states, and describes the semiconductor surface in terms of a spin-dependent energy distribution function. The so-called surface spin-splitting can be calculated from the balance of the polarized electron and hole flow in the semiconductor subsurface region, the polarized tunnelling current across the tunnel barrier between the magnetic material and the semiconductor surface, and the spin relaxation at the semiconductor surface. Measurements are presented of the circular-polarization-dependent photocurrent (the so-called helicity asymmetry) in thin-film tunnel junctions of Co/Al2O3/GaAs. In the absence of a tunnel barrier, the helicity asymmetry is caused by magneto-optical effects (magnetic circular dichroism). In the case where a tunnel barrier is present, the data cannot be explained by magneto-optical effects alone; the deviations provide evidence that spin-polarized tunnelling due to optical spin orientation occurs. In Co/ tau -MnAl/AlAs/GaAs junctions no deviations from the magneto-optical effects are observed, most probably due to the weak spin polarization of tau -MnAl along the tunnelling direction; the latter is corroborated by band structure calculations. Finally, the application of photoexcited GaAs for spin-polarized tunnelling in a scanning tunnelling microscope is discussed.