Theoretical Studies Of Physical Properties In Self-assembled Quantum Dots And Rings

As we understand the world coming deeper and deeper, researching on the mi-cro world plays an absolutely necessary role. At the end of 20th century, technologyon nano-scale successfully stimulated the others technology. As a nano-material, theQuantum Dots(QDs) has been applied to optics and optoelectronic. It also have anprospective application on information storage and quantum computer.Meanwhile, another nano-structure have been fabricated in experiment,"quantumrings"(QRs). Due to the non-simply connected topology, QRs are found to have quitedifferent energy structures from the QDs, and show peculiar optical features.In this thesis, we will introduce the basic concepts of QDs and QRs, including theirgrowth process, their electronic, optical properties and their applications on quantuminformation science. Our content includes:1. Uniaxial stress modulation of excitonic fine structure splitting in QDs.We derive a simple relation between the fine structure splitting (FSS) and the po-larization angle of the exciton emission lines of self-assembled QDs under uniaxialstress. We show that the FSS lower bound under external stress can be predicted by thepolarization angle and FSS under zero stress. The critical stress can also be determinedby monitoring the change of exciton polarization angle. The work provide a usefulguidance for selecting QDs with smallest FSS which is crucial for entangled photonsources applications.2. Single-particle energy structure and peculiar excitonic spectra in QRs.We investigate the geometry, electronic structure and optical transitions of a self-assembled InAs/GaAs QR, changing its shape continously from a lens-shaped QD toa nearly one dimensional ring. We find that the biaxial strain in the QRs are stronglyasymmetric in the plane perpendicular to the QR growth direction, leading to giantoptical anisotropy in excitonic spectra.3. Unique spectral properties of exciton complexes in QRs.We investigate the temperature dependent photoluminescence PL spectra of ex-citon complexes in the self-assembled InAs/GaAs QRs. We find, unlike in QDs, thebiexciton XX and positive trion X~+ in QRs show multitransition peaks even at verylow temperatures, and the PL spectra are very sensitive to the temperature. The peculiartemperature dependent spectra of XX and X~+ is due to the unique electronic structures and the strong many-body correlation effects in the QRs.4. Hidden correlation in QDs and QRs.We show through analytical and numerical methods that the transition energiesof the exciton complexes in QDs and rings follow a simple and robust rule, i.e., thesum of exciton and biexciton transition energies minus the transition energies of trionsis always positive and remarkably constant for a large range of self-assembled QDs.More interestingly, this quantity show a sharp transition when the topology changefrom a dot to a ring. This hidden correlation effect, directly measurable in experiments,offers a useful way to understand the photoluminescence spectra of self-assembled QDsand rings.