摘要

在這篇論文中，我們對於准一維半導體系統中的自旋傳輸做了理論的研究及數值的模擬，能夠實現一個的以自旋過濾的方式產生自旋極化的原件是我們的主要目的。我們在准一維半導體系統中，考慮了Rashba自旋軌道耦合的效應、次能帶的耦合及通道中摻雜磁性雜質的影響並研究在這樣的准一維系統中的自旋傳輸性質。

我們設定InAs准一維通道的側向寬度大約是40nm，並透過閘極電壓在通道上加入一個位障/位能井，位障/位能井長度可以決定在100nm至600nm的範圍左右，而通道中磁性雜質的影響包含兩個部分：(1)磁性部分，代表了由磁性雜質磁矩所造成的部分，會在散射的過程中影響電子的自旋並造成自旋的翻轉。(2)非磁性部分，代表了由磁性雜質的帶電所造成的部分，吸引、排斥或中性都是可能的情形，而在散射的過程中並不影響電子的自旋。我們發展一套理論以計算電子在通過通道時的自旋傳輸並呈現出計算的數據結果，最後，我們發現磁性雜質的磁矩方向及帶電的性質將是影響自旋過濾的關鍵，而藉由調控閘極電壓改變位障/位能井的強度的方法，提供了一個直接且有效率的方法將自旋過濾的效果達到最佳化。

Abstract

This thesis presents a theoretical study and numerical simulation of spin transport in a quasi 1D semiconductor system. The main purpose of this thesis is to achieve a spin filtering device to generate spin polarization. Specifically, we investigate the spin transport under the effects of both the Rashba spin-orbit and the subband coupling as well as under the influence of a magnetic impurity in the wire.

In this thesis, we examine a quasi-one dimensional InAs wire with wire width about 40nm. A potential barrier/ well is introduced in the wire by using a gate voltage, with the length of barrier/ well width varying from 100 to 600 nm. The magnetic impurity includes two parts: (i) the spin-flip part, meaning the impurity magnetic moment part, which can flip the electron spin during scattering, and (ii) the non-flip part, meaning the coulomb part, which can be attractive, repulsive or neutral, and conserves the electron spin during scattering. A theory is developed to calculate the spin-dependent electron transmission through the wire, and numerical data are presented. The direction of the magnetic moment and the sign of the non-flip part are found to be critical to the spin filtering. The barrier height / well depth can be tuned via the electric gate, providing a direct and efficient means to optimize the filtering.

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