Spin Filtering In Hybrid Ferromagnetic Schottky-metal And Semiconductor Nanostructure

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.