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Spin diffusion of a spin-polarized two-dimensional electron system in semiconductor heterostructures

半导体异质结构中自旋极化二维电子系统的自旋扩散

基本信息

批准号：
11640307
负责人：
TAKAHASHI Yutaka
金额：
$ 2.18万
依托单位：
YAMAGATA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11640307/
关键词：
Quantum Well Electron Gas Spin Transport Spin Relaxation Spintronics

项目摘要

We have investigated spin tranport properties of a two-dimensional electron gas (2DEG) in heterostructures of III-V semiconductors by numerically solving the quantum transport equation. It is shown that the 'spin-rotation term', which leads to anomalous spin diffusion and spin waves in three-dimensional rarefied spin polarized ^3He and Hydrogen, is also present in two-dimensional degenerate electron systems at low temperatures. Calculated longitudinal and transverse spin diffusion coefficients show different temperature dependence due to the fact that the phase space available in electron-electron scatterings associated with each diffusion process is different.In 2DEG of the actual semiconductors, in addition to electron-electron (e-e) scattering, electron-impurity scattering, which is not included in the present theory, also affects the spin diffusion.The frequent e-impurity scattering could prevent us from observing the effects of e-e scattering predicted in our calculations. We have estimated the contribution of e-impurity scattering to the spin diffusion from the experimental carrier mobilities by the generalized Einstein's relation. The estimation shows that both e-impurity and e-e scatterings have comparable contributions in the high mobility samples at low temperatures (< 10 K), indicating we need very high-quality samples to observe 'spin-rotation effects'.We have started measuring spin diffusion and spin relaxation in AlGaAs/GaAs/InGaAs quantum wells. The spin-polarized electrons are photogenerated in the front AlGaAs layer, then they drift through the pn junction, and captured in the InGaAs well to radiative decay. The preliminary time-resolved polarization measurements show that electrons are partially spin-relaxed before they reach the bottom of the well. The structural or material optimization is requisite to obtain a highly spin-polarized electron gas.

通过数值求解量子输运方程，研究了III-V族半导体异质结构中二维电子气的自旋输运性质。结果表明，导致三维稀薄自旋极化^3He和氢的反常自旋扩散和自旋波的“自旋-转动项”在低温下也存在于二维简并电子系统中。计算的纵向和横向自旋扩散系数显示出不同的温度依赖性，这是由于与每个扩散过程相关的电子-电子散射中可用的相空间不同。在实际半导体的2DEG中，除了电子-电子（e-e）散射，电子-杂质散射，频繁的电子杂质散射可能会阻碍我们观察到我们计算中预测的电子杂质散射效应。本文从实验载流子迁移率出发，用广义爱因斯坦关系估计了电子杂质散射对自旋扩散的贡献。计算结果表明，在低温（< 10 K）下，高迁移率样品中的电子杂质和电子-电子散射的贡献相当，这表明我们需要非常高质量的样品来观察“自旋-旋转效应”。自旋极化的电子在前面的AlGaAs层中光生，然后它们漂移通过pn结，并在InGaAs阱中被捕获以辐射衰减。初步的时间分辨极化测量表明，电子到达阱底之前是部分自旋弛豫的。结构或材料优化是获得高自旋极化电子气所必需的。