Manipulation Of Magnetoresistance Effect In Magnetically Confined Semiconductor Heterostructures

Magnetoresistance?MR?effect has always been an important research direction in the fields of condensed matter physics,materials science and magneto-electronics due to its own scientific significance and important applications in magnetic information storage such as random access memory,high-density read heads,and ultra-sensitive magnetic field sensors.Generally,the MR effect is observed in a"sandwich"structure consisting of"magnetic layer-nonmagnetic layer-magnetic layer",and the magnetoresistance ratio is used to characterize the MR effect,which is defined asMRR?28?(G_P-G_AP)/G_APor(G_P-G_AP)/(G_P?10?G_AP),whereG_P andG_AP are the conductance of the parallel?P?and antiparallel?AP?magnetized configurations,respectively.It is generally believed that the mechanism of MR effect is spin related scattering—in the P configuration,the spin related scattering is the weakest with maximum conductivity,while in the AP configuration,the spin related scattering is the strongest with minimum conductivity.However,in 2002,research has found that the MR effect which is not associated with the spin scattering in magnetically modulated semiconductor heterostructures from the significant difference in electron transport between P and AP magnetization configurations,and the magnetoresistance ratio is very high?up to 10⁶%order of magnitude?under a small switching magnetic field.Therefore,such semiconductor-based MR device is expected to replace the traditional matel-based MR device,which has become a frontier hotspot in MR effect research in recent years.For practical applications,it is desirable for MR devices to have a high and controllable magnetoresistance ratio.This paper uses a combination of theoretical analysis and numerical calculation to investigate MR effect in a typical magnetically confined semiconductor heterostructure?MCSH?,explore new methods of manipulation of semiconductor-based MR devices,and build controllable semiconductor-based MR devices for magneto-electronics applications.The full text consists of six chapters.The first chapter introduces the research of MR effect,magnetically modulated semiconductor heterostructure and its MR effect,and the research content of this paper.The second chapter introduces the research methods used in this paper,including the improved transfer matrix methodand the Landau-Büttiker conductance theory.In chapter 3,we study the influence of Delta-doping on the MR effect in MCSH structures.In Chapter 4,we explore the manipulation of the MR effect in MCSH structure by external electric field or applied bias.Chapter 5 discusses the effect of electron spin on the MR effect in MCSH structure.The sixth chapter is the summary and outlook,summarizes the research results of this thesis,points out the shortcomings in the research and prospects for future research.The results of this thesis mainly have the following four aspects:?1?After embedding a Delta-doping,a significant MR effect still exists in the MCSH structure,because Delta-doping does not change the formation mechanism of the MR effect in the magnetically modulated semiconductor nanostructure.However,since the effective potential felt by electrons in the MCSH structure is closely related to Delta-doping,the MR ratio can be effectively adjusted by changing the weight or position of Delta-doping.?2?When a bias voltage is applied to the MCSH structure,a transverse electric field will be generated in the direction of electron transport and a MR effect still exists in the MCSH structure.The reason is that the bias voltage or transverse electric field will not change the mechanism of MR effect in magnetic modulation semiconductor nanostructures.However,the effective potential experienced by electrons in the MCSH structure depends on the lateral electric field or bias,so we can effectively control the MR ratio by changing the strength or direction of the lateral electric field.?3?If the spin of electrons is involved,the spin-field interaction?Zeeman coupling?between the spin and the magnetic field changes the effective potential of the electrons in the MCSH structure,resulting in electron transmission or conductance through the P and AP magnetization configurations depend on the spin of electrons.Therefore,the spin splitting phenomenon of the MR effect appears in the MCSH structure,and the degree of spin splitting of the MR effect can be effectively adjusted by changing the level or polarity of the bias.?4?In this way,the MCSH structure can be used as a new type controllable MR device in magneto-electronics applications,and its magnetoresistance ratio can be effectively adjusted by changing the SM stripe,Delta-doping,external electric field or bias voltage in the structure.Therefore,the results of this study can not only provide an effective way to realize the manipulation of semiconductor-based MR devices,but also the MCSH structure can be used for controllable MR devices in the field of magnetic information storage.