Electron-spin Polarization And Its Manipulation In 3-layered Semiconductor Heterostructures

Semiconductor spintronics is an emerging multidisciplinary field combining microelectronics with magnetics,and mainly investigates generation and manipulation of electron-spin polarization in semiconductors.Due to itself scientific significance and potential applications in spintronics devices such as spin field-effect transistor(SFET)and spin resonant tunneling diode(SRTD),spin-orbit coupling(SOC)effect,electron-spin polarization and its manipulation in layered semiconductor heterostructure(LSH)became a hot topic in semiconductor spintronics in recent years.Adopting theoretical analysis combining with numerical calculation,in this thesis,we study two different kinds of SOC effects(Rashba and Dresselhaus types)in3-layered semiconductor heterostructure(3-LSH),and explore electron-spin polarization as well as its control in semiconductors,focusing on developing tunable electron-spin filter as controllable spin-polarized source for semiconductor spintronics device applications.The whole thesis consists of five chapters.In chapter 1,we briefly introduce the research field of semiconductor spintronics,the progress of electron-spin polarization and its control in LSHs,and the specific research content of this thesis.The theoretical basis and research methods adopted in this thesis are introduced in chapter 2,including SOC effect,diagonalization technique and improved transfer matrix method.In chapter 3,we study the Rashba-SOC effect in 3-LSH,the electron-spin polarization and its control via ?-doping.Next,the Dresselhaus-SOC effect induced electron-spin polarization and its manipulation by?-doping in 3-LSH are explored in chapter 4.Finally,we summarize research results of the full thesis,point out its shortcomings and prospect for future research.The results obtained in this thesis mainly contain three aspects as follows:(1)It is found that,due to Rashba-SOC effect,an obvious electron-spin polarization appears in 3-LSH.Degree of spin polarization is closely related to in-plane wave vector,Rashba-SOC strength,intermediate-layer semiconductor and ?-doping.Both magnitude and sign of electron-spin polarization can be manipulated by changing the position or weight of?-doping,tuning interfacial confining electric field or fabricating a proper intermediate layer.(2)It is found that,Dresselhuas-SOC effect can also make electrons in3-LSH produce considerable spin polarization.The electron-spin polarization depends strongly on in-plane wave vector,Dresselhaus-SOC effect and ?-doping.The behavior of spin-polarized electrons can be controlled by strain engineering,appropriately constructing an intermediate layer and adjusting weight or position of ?-doping.(3)The 3-LSH can serve as a controllable electron-spin filter,and its spin polarization ratio can be effectively manipulated by changing interfacial confining electric field or strain engineering,constructing a proper intermediate-layer semiconductor and adjusting ?-doping.This research not only can propose an effective scheme to realize the spin polarization of electrons in semiconductor materials,but also can achieve a tunable spin-polarized source---electron-spin filter for semiconductor spintronics device applications.