Study Of Structures And Electrostatic Properties Of In As Quantum Dots Decorating GaAs/ALAs Core/Shell Nanowires

?-? compound semiconductor materials have gained more and more attention in the field of nano-photodetectors due to their characteristics of high carrier mobility,high thermal conductivity,easy doping,and adjustable band gap.In recent years,many related studies have reported further improvements in the performance of nanodevices by introducing quantum dots and quantum wells into nanowires to form heterostructures.With a wide range of applications,stable and controllable process of synthesis,heterostructural GaAs nanowires have become ideal research objects.However,there are few reports on the underlying mechanism of performance improvement due to the introduction of heterostructures in GaAs nanowires,especially at nanoscale.With transmission electron microscope as the carrier and various related techniques as the supporter,transmission electron microscope is a powerful tool for studying the morphology,structure and composition of materials at nanoscale.It has been widely used in research of many nanocrystalline materials.Electron holography,as an important technique of transmission electron microscopy,is capable of studying the electrostatic field,strain,and magnetic field distributions of materials at nanometer scale,making it possible to effectively characterize the electrostatic properties of heterostructural nanowires at nanometer scale.In this thesis,the InAs quantum dots decorating GaAs/AlAs core-shell nanowires are selected as the research object,transmission electron microscopy and density functional theory are utilized to quantitively studied the structure and electrostatic properties of the heterostructural nanowires at nanometer scale.The major results and conclusions are as follows:1.GaAs nanowires of high crystal quality are prepared by metal organic chemical vapor deposition,periodically grown quantum dots are observed at one side of nanowire from high resolution transmission electron microscope images;locations of the interfaces are determined through electron energy-dispersive spectrum analysis,C doping is detected in InAs quantum dot region;geometric phase analysis reveals compressive strain in the InAs quantum dot region and tensile strain in the GaAs/AlAs core-shell nanowire region,and the strain fields are anisotropic.2.Electron holography is carried out to analyze the electrostatic properties of heterostructural nanowires at nanoscale: a large number of electrons accumulate in the InAs quantum dot region due to n-type doping of C;charges of reversed signs and similar densities are observed to distribute at the sequential interfaces;a great amount of holes accumulate in the NW core to meet the requirement of overall charge neutralization;overall energy band is calculated,and it turns out that the energy band is slightly tilted,forming type-I energy band structure,electrons transfer from GaAs layer to AlAs layer,and fianlly gather at InAs layer,which fits well with the electron holography results.3.Charge migration and interactions of interfaces are studied through first principles calculation,and the calculated charge migration route agrees well with the experimental results.Interaction calculations of interfaces show that the introduction of Al As buffer layer enhances the adhesion of InAs quantum dots on nanowire surfaces,forming stable quantum dot/nanowire heterostructure system.