铁磁、肖特基金属和半导体复合纳米结构中的电子自旋过滤
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摘要
自旋电子学是一门新兴的交叉学科,其主旨是对固态系统中的自旋自由度进行有效的操作和调控,将自旋自由度和半导体工艺相结合制造新型的自旋电子器件。利用电子的自旋来制造自旋电子器件的前提条件是使半导体中的电子发生自旋极化以及半导体纳米结构中电子自旋的限域和输运。本论文将就铁磁、肖特基金属和半导体复合纳米结构中电子的自旋输运问题在理论上作较为深入、系统的研究。
全文共五章。第一章为绪论部分,简要介绍了自旋电子学的研究领域,主要包括实验上和理论上需要解决的重大问题,目前的研究进展以及在半导体仪器方面的应用前景等。然后,介绍磁调制半导体纳米结构的制备及磁调制半导体纳米结构中电子自旋输运的研究动态。
第二章我们研究了由Guo等人提出的自旋过滤器中,器件的结构参数(如铁磁条带的宽度和厚度,肖特基金属条带的宽度,两条带之间的间距等)对电子自旋过滤性质的影响。该自旋过滤器可以通过在半导体异质结表面上沉积纳米尺度的铁磁条带和肖特基金属条带来实现。研究表明,电子的自旋过滤特性与铁磁条带和肖特基金属条带的结构尺度及位置密切相关,因此该器件中存在量子尺寸效应。此外,我们的研究还发现,电子的自旋极化率会随着电垒高度(由施加在肖特基金属条带上的电压产生)的变化剧烈变化。因此可以通过调节施加在肖特基金属条带上的电压来调控该自旋过滤器中电子的自旋极化行为。
第三章,在前一章的基础上研究了偏压对该自旋过滤器中电子自旋极化特性的影响。研究结果显示,偏压不仅能明显改变电子的自旋极化率而且还能使自旋极化的符号发生变化。因此可以通过调节施加在该器件上的偏压来调控该器件中电子的自旋极化率,制造一个偏压可调的电子自旋过滤器。
第四章中,我们通过在前面的自旋过滤器上再沉积一条铁磁条带,对该自旋过滤器进行了进一步优化,提出了另一个电子自旋过滤器,同时在该器件上施加偏压,探究了偏压对该器件中电子自旋极化特性的影响。研究发现,该自旋过滤器中电子的自旋极化率与偏压密切相关。这一结果暗示人们可以通过调节施加在该器件上的偏压来改变电子的自旋极化率,这对制作偏压可调的电子自旋过滤器十分有益。
Spintronics is a multidisciplinary field whose central theme is the active manipulation of spin degrees of freedom in solid-state systems, and make useful spintronics devices using the spin degrees of freedom and semiconductor technology. The realization of the spintronics devices, a very important requirement is the realization of spin-polarized electrons into semiconductors, as well as confinement of electron spins and transport of spin-polarized electrons in semiconductor nanostructures. In this thesis, we present systematically the theoretical investigation of the spin-dependent electron transport in ferromagnetic-Schottky-stripe and semiconductor nanostructures.
The thesis is made up of five chapters. Chapter one is an introduction, in this part, we first introduces the spintronics including major problems that need to resolve both in experiment and theory, some established results, and potential applications to electronic devices. We then introduce the preparation of magnetically modulated semiconductor nanostructures and present some published results on the electron-spin filter in this kind of nanostructures.
In chapter two, we study the effect of structural parameters on electron-spin polarization in a spin filter proposed by Guo et al., which can be realized by depositing nanosized ferromagnetic metal stripe and Schottky normal metal stripe on the top of the semiconductor heterostructure. It is shown that the spin polarization is dependent greatly on the sizes and position of the stripes. Thus, a quantum size effect exists in this device. It is also shown that the spin polarization can be altered by adjusting the voltage applied to the Schottky normal metal stripe, and thus one can control spin-polarized electrons by adjusting this applied voltage on the Schottky normal metal stripe of the system.
In chapter three, based on the previous chapter, we investigated the effect of the bias on the spin polarization in the same spin filter. It is shown that not only the amplitude of the spin polarization but also its sign varies with the bias. Thus, the spin filtering in this device can be controlled via the bias, giving rise to a bias-tunable spin filter.
In chapter four, a spin filter will be realized by depositing nanosized ferromagnetic metal stripe, Schottky normal metal stripe and ferromagnetic metal stripe on the top of the semiconductor heterostructure. We study the effect of the bias on the spin-dependent transport properties of electrons in this spin filter by adding bias on this device. It is shown that the spin polarization of this spin filter is closely related to the applied bias. These interesting properties tell us that we can change the spin polarization of the electrons by altering the voltage applied to the device, and it is very valuable to make a bias-tunable electron-spin filter.
全文共五章。第一章为绪论部分,简要介绍了自旋电子学的研究领域,主要包括实验上和理论上需要解决的重大问题,目前的研究进展以及在半导体仪器方面的应用前景等。然后,介绍磁调制半导体纳米结构的制备及磁调制半导体纳米结构中电子自旋输运的研究动态。
第二章我们研究了由Guo等人提出的自旋过滤器中,器件的结构参数(如铁磁条带的宽度和厚度,肖特基金属条带的宽度,两条带之间的间距等)对电子自旋过滤性质的影响。该自旋过滤器可以通过在半导体异质结表面上沉积纳米尺度的铁磁条带和肖特基金属条带来实现。研究表明,电子的自旋过滤特性与铁磁条带和肖特基金属条带的结构尺度及位置密切相关,因此该器件中存在量子尺寸效应。此外,我们的研究还发现,电子的自旋极化率会随着电垒高度(由施加在肖特基金属条带上的电压产生)的变化剧烈变化。因此可以通过调节施加在肖特基金属条带上的电压来调控该自旋过滤器中电子的自旋极化行为。
第三章,在前一章的基础上研究了偏压对该自旋过滤器中电子自旋极化特性的影响。研究结果显示,偏压不仅能明显改变电子的自旋极化率而且还能使自旋极化的符号发生变化。因此可以通过调节施加在该器件上的偏压来调控该器件中电子的自旋极化率,制造一个偏压可调的电子自旋过滤器。
第四章中,我们通过在前面的自旋过滤器上再沉积一条铁磁条带,对该自旋过滤器进行了进一步优化,提出了另一个电子自旋过滤器,同时在该器件上施加偏压,探究了偏压对该器件中电子自旋极化特性的影响。研究发现,该自旋过滤器中电子的自旋极化率与偏压密切相关。这一结果暗示人们可以通过调节施加在该器件上的偏压来改变电子的自旋极化率,这对制作偏压可调的电子自旋过滤器十分有益。
Spintronics is a multidisciplinary field whose central theme is the active manipulation of spin degrees of freedom in solid-state systems, and make useful spintronics devices using the spin degrees of freedom and semiconductor technology. The realization of the spintronics devices, a very important requirement is the realization of spin-polarized electrons into semiconductors, as well as confinement of electron spins and transport of spin-polarized electrons in semiconductor nanostructures. In this thesis, we present systematically the theoretical investigation of the spin-dependent electron transport in ferromagnetic-Schottky-stripe and semiconductor nanostructures.
The thesis is made up of five chapters. Chapter one is an introduction, in this part, we first introduces the spintronics including major problems that need to resolve both in experiment and theory, some established results, and potential applications to electronic devices. We then introduce the preparation of magnetically modulated semiconductor nanostructures and present some published results on the electron-spin filter in this kind of nanostructures.
In chapter two, we study the effect of structural parameters on electron-spin polarization in a spin filter proposed by Guo et al., which can be realized by depositing nanosized ferromagnetic metal stripe and Schottky normal metal stripe on the top of the semiconductor heterostructure. It is shown that the spin polarization is dependent greatly on the sizes and position of the stripes. Thus, a quantum size effect exists in this device. It is also shown that the spin polarization can be altered by adjusting the voltage applied to the Schottky normal metal stripe, and thus one can control spin-polarized electrons by adjusting this applied voltage on the Schottky normal metal stripe of the system.
In chapter three, based on the previous chapter, we investigated the effect of the bias on the spin polarization in the same spin filter. It is shown that not only the amplitude of the spin polarization but also its sign varies with the bias. Thus, the spin filtering in this device can be controlled via the bias, giving rise to a bias-tunable spin filter.
In chapter four, a spin filter will be realized by depositing nanosized ferromagnetic metal stripe, Schottky normal metal stripe and ferromagnetic metal stripe on the top of the semiconductor heterostructure. We study the effect of the bias on the spin-dependent transport properties of electrons in this spin filter by adding bias on this device. It is shown that the spin polarization of this spin filter is closely related to the applied bias. These interesting properties tell us that we can change the spin polarization of the electrons by altering the voltage applied to the device, and it is very valuable to make a bias-tunable electron-spin filter.
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