Semiconductor Spintronics

The following sections are included:

• PREFACE

• LIST OF ACRONYMS

• CONTENTS

Spintronics studies the use of spin freedom of electrons. It originated from the giant magnetic resistance (GMR) effect found by Fert and Gruenberg, respectively, in 1988. This discovery produced highly sensitive magnetic sensors, used in the read-out head of the magnetic hard disk. Just after 9 years as the GMR was discovered, in November 1997 IBM Co. declared that they fabricated the commercial read-out head of the magnetic hard disk. This product accomplished an enterprise of several billions of US dollars. The spin electronic devices under study include magnetic random access memory (MRAM), spin field effect transistor (FET), spin-polarized laser, etc. These devices depend on their ability to control spin in the solids and they can be used to decrease the power consumption, to overcome the velocity limit connected with the charge electrons, and in the quantum information treatment and quantum computation in future…

The following sections are included:

• Electron Configuration of Magnetic Ions

• Splitting of the Basis State of Free Ions in the Crystal Field

• Crystal Field Theory

• Wave Functions of Many-electron States

• Equivalent Operator Method

• Magnetic Ion Energy Levels in Semiconductors

• Experimental Study of the Properties of Magnetic Ions in Semiconductors

• References

The semiconductors doped with magnetic ions form a new kind of ternary alloys having magnetic properties. Because the concentration of the doped magnetic ions is generally not high, and the magnetic properties are not strong, they are called DMS, or semimagnetic semiconductors. The crystalline structures, concentration ranges, and energy gaps of some DMSs are listed in Table 2.1 (Liu and Zhang, 1994), where ZB represents the zincblende structure and WZ the wurtzite structure…

Ferromagnetism in magnetic semiconductors has been studied widely several tens of years ago, for example, CdCr₂Se₄, EuO, and sulfide compounds of lead (Pb_1-x-ySn_yMn_xTe), etc. Recently, ferromagnetism has been discovered in Mn-doped III–V compounds, such as In_1-xMn_xAs (Ohno et al., 1992), and Ga_1-xMn_xAs (Ohno et al., 1996). These magnetic compounds attract utmost interests as they combine the two large branches in condensed matter physics: semiconductor and magnetism. They are also attractive from the technological point of view, since they can add a new degree of freedom associated with the spin of carriers to the electronic as well as optical semiconductor devices. The experiment found that the Curie temperature in Ga_1-xMn_xAs, x ~ 0.05 reaches as high as 110K (Matsukura et al., 1998)…

The following sections are included:

• Spin Lifetime and Drift of Electrons in Semiconductors

• Rashba Effect

• Semiconductor Spin Transistor and Quantum Waveguide Theory

• Quantum Waveguide Theory of Rashba Electrons

• Generation and Transport of Spin-polarized Current

• Magnetic Semiconductor Tunneling Junction

• References

The following sections are included:

• SRTs T₁ and T₂

• Elliot–Yafet Relaxation Mechanism

• Dyakonov–Perel Relaxation Mechanism

• Bir–Aronov–Pikus Mechanism

• Experimental Studies of Spin Relaxation in III–V Compounds

• Spin Relaxation in Quantum Wells

• Electron Spin Relaxation Studied by a Kinetic Spin Bloch Equation

• References

The following sections are included:

• Spin Splitting Induced by Spin–Orbit Interaction (SOI) in Inversion Asymmetrical Semiconductors — Rashba and Dresselhaus Effects

• The SOI Hamiltonian in a Rashba System

• The Rashba Effect and Dispersion (Feve et al., 2002)

• Rashba Parameter α

• Deriving the Rashba Coefficient α from the SdH Oscillation

• Spin-related Scattering and Spin Current

• References

In Chap. 6, we have introduced the lift-up effect of the spin degeneration due to SOI, and the consequent appearing of a linear term of vector k in the electron Hamiltonian. The splitting of the electron spin states has a fundamental significance in spintronics, as it provides a possibility of controlling the electron spin polarization by electric field and affects the rate of spin relaxation. In particular, as shown below, it might be applied to all-electric circuit for spin injection without an external magnetic field (Fabian and Das-Sarma, 2004)…

The following sections are included:

• Experimental Methods

• Electron Spin Coherence in Semiconductor Bulk Materials

• Electron Spin Coherence in Semiconductor QDs

• Spatial Movement of Spin Coherent Electrons in Semiconductors

• Spin Hall Effect

• Generation of Spin Current

• Spin Dynamics in Semiconductors

• Coherent Manipulation of a Single Spin in Semiconductors

• Spin Polarization and Transport in Silicon

• References

The following sections are included:

• Spin Transport in Magnetic Semiconductor 2DEG

• Spin Transport Through QDs

• Magnetic Domain Transport in Magnetic Semiconductors

• References

Quantum computation and quantum communication need to design necessary hardware. Loss and DiVincenzo (1998) showed that the spin qubits in the quantum confinement systems, such as semiconductor QDs, atoms, or molecules satisfy all demands of scalable quantum computers. Besides, if the spin qubit is adhered at a movable electron, it can transport along the conductor. An interesting application of this possibility is the production (for example, in the coupled QDs or superconductor–normal metal interface) and transport of spin-entangled electrons, which is called Einstein–Podolsky–Rosen pair. The scheme of quantum computer based on the QD spins proposed by Loss and DiVincenzo (1998) is shown in Fig. 10.1. The system is composed of a magnetization layer or a high g layer, a modulation-doped heterojunction layer (2DEG), and surface and bottom gate arrays. The QDs can be formed by applying voltage on the gates, as shown by the circles in Fig. 10.1. Changing the gate voltage, the electrons can enter into the magnetization layer or the high g layer. A localized magnetic field can be produced by the electric current flowing in the left conductor. The electron spin in each QD can be set up individually through the ESR pulse produced by the alternating magnetic field in the plane. This mechanism can be used to produce initiation and rotation of spins. The exchange coupling between QDs is controlled by lowering the tunneling barrier between dots…

The following sections are included:

• INDEX