Based on a tight-binding study of the electronic spin structure in self-assembled InGaAs/GaAs quantum dots, we propose a theory to explain why the electron g factor in these artificial atoms is insensitive to the variation of the structural dimensions and chemical composition profile and also present a microscopic picture to understand the isotropic behavior of the lateral electron g factor. The former provides an important justification for the recent experimental measurement of electron g factors in an ensemble of quantum dots, while the latter overrides the common knowledge that the shape anisotropy of quantum dots has an important effect on the in-plane electron g-factor anisotropy.

Linear polarization of the multiexciton emission from self-assembled quantum dots is investigated by using an empirical tight-binding method. The polarization of the primary interband transition is shown to have a quadratic dependence on the lateral aspect ratio of the structures and is insensitive to both the excitonic and random intermixing effects, which make it an appropriate tool for structure characterization. The ground-state transitions in the emission spectra of multiexciton complexes are found to exhibit very different polarization from the primary interband transition, which we attribute to different component profiles in the excited valence-band states.

Intersubband transitions in self-assembled quantum dots are studied by using a multiband tight-binding method. A picture different from that by the single-band effective-mass approximation is presented to reveal the origin of the polarization of the intersubband transitions. It is shown that the symmetry of those minor components from the valence bands in the electronic states accounts for the polarization of the intersubband transitions. A microscopic theory is presented to explain the pattern of symmetry of these minor components in the electronic states. The result is compared with a recent experiment. © 2008 American Institute of Physics.

We point out using an empirical tight-binding approach that the ground state of holes in InAs/GaAs self-assembled quantum dots carries nonzero orbital momentum. The spin and orbital motions of the hole state are found to have opposite contributions to the hole g factor, leading to zero g factors of holes and then excitons in dots of high aspect ratio. The nonzero envelope orbital momenta of the holes are also shown to account for anisotropic circular polarization of exciton emission and nonlinear Zeeman splittings in high magnetic fields. Our theory well explains recent experiments and indicates the possibility of engineering magnetic splitting by tuning the electric confinement in nanostructures.

The author report on a theoretical study of optical anisotropy in quantum dots. The mechanisms how shape anisotropy and strain field lead to optical anisotropy are identified by an empirical tight-binding approach. The anisotropic structure of quantum dots is shown to impose stronger confinement for the localized p orbitals aligning along the short axis. In self-assembled quantum dots, these orbitals are also seen in a higher potential produced by the strain field. As a result, the valence-band electrons prefer to occupy the orbitals aligning along the long axis, which leads to stronger optical emission polarized along that direction. © 2006 American Institute of Physics. _DOI: 10.1063/1.2370871-Opti