Effects Induced By Different Spin-Orbit Couplings In Spin Transistor And Spin Injection

Since the discovery of the giant magnetoresistance effect in Fe/Cr multilayer structures in 1988, the spin-related phenomena have been one of the important frontiers. This leads to open a new research field named spintronics. In spintronics, the electrons have not only charges but also spins. Introducing the new degree of freedom makes the research content rich and it provides a new source to design the new-type devices.Electronic spin transport is one of the hot topics in spintronics. It is mainly because of spin transport having potential application in semiconductor electronics and quantum computing. The modulation and control of spin-polarized current is an important aspect of spin transport. Recently there is a good opportunity to use the spin-orbit coupling in the low-dimensional semiconductors for spin transport. In these systems, one usually uses the external parameters to control the spin-polarized phenomena.The spin injection to semiconductor plays a decisive role in realizing the spintronics devices. It is also a bottleneck of the constraint of its applications. Thus it remains a challenge to find the efficient way and method to obtain high spin-injection rate. The spin field-effect transistor proposed by Datta and Das is a major step in spintronics device, and it is one of important research topics now.In this thesis, using quantum-mechanics method and Landauer conductance formula, we studied the spin-dependent properties of the following two systems: one is the heterostructure consisting of the metallic ferromagnet and the quantum wires with different Rashba spin-orbit couplings, and the other is the spin field-effect transistor with different Rashba spin-orbit couplings.(1) Considering the spin polarization in metallic ferromagnet, the interfacial scattering, the band mismatch and different Rashba spin-orbit couplings in two quantum wires, we studied the conductance and spin injection in the Ferromagnet/Semiconductor1/Semiconductor2 structure within the framework of quantum mechanics. It was shown that the spin injection efficiency of our system can be reduced or enhanced if additional interface scattering potential is increased. Also we found that the spin injection efficiency can be enhanced if we adjust the band structure mismatch suitably. In addition, we can obtain the optimum spin injection efficiency at the suitable combination of the two spin-orbit coupling strengths. (2) By using quantum mechanics approach and considering ballistic transport, we theoretically studied the conductance, spin injection and tunnelling magnetroresistance effect in spin field-effect transistor with different Rashba spin-orbit couplings. It was shown that the conductance not only has the fixed peak but also has the movable peak in reasonable range of Rashba spin-orbit coupling strength. The spin injection efficiency oscillates quasi-periodically with the two different Rashba spin-orbit strengths.. By tuning the two different Rashba spin-orbit strengths, we can easily achieve the switching between positive and negative tunneling magnetoresistance. These transport properties are strongly dependent on the two different Rashba spin-orbit strengths. Through the two gate voltages, the conductance, spin injection efficiency and the tunneling magnetoresistance can be controlled and modulated.