Nanometer-scale Study Of Electrostatic Properties In GaAs/AlGaAs Single Quantum Well/nanowire Heterostructures By Transmission Electron Microscopy

With the development of semiconductor nanotechnology and the potential need for highly integrated optoelectronic devices,III-V compound semiconductors with excellent physical and chemical properties begin to replace original bulk materials,and play increasingly important role in the field of optoelectronics.GaAs and AlGaAs are two common materials of III-V compound semiconductors.GaAs/AlGaAs nanowire heterostructures with unique structures and superior performances have become one of the hottest research topics.Nanowire heterostructures with an embedded GaAs quantum well have drawn much attention from researchers due to their novel electronic states and outstanding photoelectric performances.While the macroscopic properties of these hybrid structures have been extensively studied,the charge distributions and underlying working mechanisms at the nanoscale have less been reported.In this thesis,GaAs/AlGaAs single quantum well/nanowire heterostructures were selected as the research object.Several transmission electron microscopy(TEM)related techniques were applied for comprehensive characterizations of the morphologies,crystal structures,elemental distributions and electrostatic properties at the nanometer scale.The main results of this study are as follows:1.Structure of the nanowire heterostructures were characterized in detail using transmission electron microscope.The results reveal that the nanowires have zinc blende crystal structure with good crystallinity,and the strain level across the GaAs/AlGaAs heterointerface is relatively low.2.Charge distributions in the vicinity of GaAs quantum well were explored by electron holography,the results of which show considerable electrons accumulating in the GaAs quantum well,leaving a large number of holes distributing around the GaAs/AlGaAs heterointerfaces.Density functional theory(DFT)calculations of the charge distributions across the hetero-interface confirm the results of electron holography.3.The simulation results of the energy band structures for GaAs bulk material and GaAs quantum well,as well as the obvious blue-shift of the GaAs peak in the photoluminescence(PL)spectra of the nanowires reveal quantum confinement effect in the GaAs quantum well.