Optical characterization of structure for semiconductor quantum dots

Abstract

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.Semiconductor self-assembled quantum dots, sometimes called artificial atoms, 1 are three-dimensional nanostructures in which carriers are confined along the three dimensions of space by the band gap difference between the dot and barrier materials. The electronic and optical properties of these nanoscale systems are affected by the strong influence of the low symmetry of the confined nanostructures and the strain due to the lattice mismatch between the different materials. Unlike natural atoms, self-assembled quantum dots take various shapes that can be either symmetric or asymmetric. Ascertaining the shape of quantum dots and other related structural parameters is of primary importance for both fundamental and practical reasons. 2 In the absence of magnetic field, the emission from quantum dots is often not isotropic with respect to its polarization direction. 3,4 Strong biaxial strain suppresses light-hole components in the valence-band states, leaving mostly heavyhole components and resulting in in-plane polarized emission from the interband transitions. 5,6 It has been shown that the linear polarization of the interband transitions in a selfassembled quantum dot originates from its shape anisotropy. 7 Due to very little difference in the dielectric constants between the quantum dot and barrier materials, the local field or depolarization effect is believed to contribute only a small portion of the overall linear polarization of the emission.Optical spectroscopy has been shown to be an appropriate tool for probing many electronic properties of quantum dots, such as the shell structure of electronic states. 8 However, for self-assembled quantum dots, a direct manifestation of geometrical anisotropy by optical spectroscopy has yet been well established, which we believe is due to the lack of an applicable theory that bridges these two aspects. In the present work, we will explore the possibility of optical characterization of structure for semiconductor self-assembled quantum dots. The proposed scheme is based on a quantitative relation established between the optical and shape anisotropies by an empirical tight-binding approach. 9,10The model system is an InAs/ GaAs quantum dot which is elongated along the ͓110͔ direction. It has a variable lateral aspect ratio ␤ = d x / d y where d x ͑=d͒ and d y are the dimensions along the long ͑x = ͓110͔͒ and sho...

Anticorrelation between the splitting and polarization of the exciton fine structure in single self-assembled InAs/GaAs quantum dots

“…[24][25][26][27][28] We show that FSS and polarization anisotropy of exciton in InAs/GaAs selfassembled QDs are correlated, but with an unexpected reversal in order of the polarization eigenaxes. Such an anticorrelation indicates that the splitting induced by the exchange interactions coupled via valence-band mixing (VBM) play an important role in the excitonic FSS in elongated QDs.…”

Polarization of emission from self‐assembled quantum dots and its application to the optical characterization of structure

“…When the electron-hole interaction is taken into account, it is shown that the polarization of the emission is not very different from the non-interacting case [16,17]. Therefore, the nearly linear dependence of the polarization on the lateral aspect ratio of the quantum dots makes the interband optical spectroscopy an appropriate tool for structure characterization.…”

Anisotropic Confinement, Electronic Coupling and Strain Induced Effects Detected by Valence-Band Anisotropy in Self-Assembled Quantum Dots

“…Due to strong valence-band admixture, such a procedure provides straightforward information on the relaxation of the inter-band optical transition selection rules, using lower computational efforts than in tight-binding calculation model, for example [13,14]. The built-in strain field distribution, which lead to the formation of self-assembled QD arrays, has been considered within the Bir–Pikus deformation potential model [21].…”