Self-organized Semiconductor Quantum Dots Research Articles

Soliton nanoantennas in two-dimensional arrays of quantum dots

We consider two-dimensional (2D) arrays of self-organized semiconductor quantum dots (QDs) strongly interacting with electromagnetic field in the regime of Rabi oscillations. The QD array built of two-level states is modelled by two coupled systems of discrete nonlinear Schrödinger equations. Localized modes in the form of single-peaked fundamental and vortical stationary Rabi solitons and self-trapped breathers have been found. The results for the stability, mobility and radiative properties of the Rabi modes suggest a concept of a self-assembled 2D soliton-based nano-antenna, which is stable against imperfections In particular, we discuss the implementation of such a nano-antenna in the form of surface plasmon solitons in graphene, and illustrate possibilities to control their operation by means of optical tools.

Combined influence of Coulomb interaction and polarons on the carrier dynamics in InGaAs quantum dots

Experimental results for the carrier capture and relaxation dynamics in self-organized semiconductor quantum dots are analyzed using a microscopic theory. Time-resolved differential transmission changes of the quantum-dot transitions after ultrafast optical excitation of the barrier states are studied in a wide range of carrier temperatures and excitation densities. The measurements can be explained by quantum-dot polaron scattering and their excitation-dependent renormalization due to additional Coulomb scattering processes. Results of configuration-picture and single-particle-picture descriptions, both with nonperturbative transition rates, show good agreement with the experiments while Boltzmann scattering rates lead to a different excitation density and temperature dependence.

Quantum Dots for Single- and Entangled-Photon Emitters

The efficient generation of polarized single or entangled photons is a crucial requirement for the implementation of quantum key distribution (QKD) systems. Self-organized semiconductor quantum dots (QDs) are capable of emitting one polarized photon or an entangled photon pair at a time using appropriate electrical current injection. We realized a highly efficient single-photon source (SPS) based on well-established semiconductor technology: In a pin structure, a single electron and a single hole are funneled into a single InAs QD using a submicron AlOx current aperture. Efficient radiative recombination leads to emission of single polarized photons with an all-time record purity of the spectrum. Non-classicality of the emitted light without using additional spectral filtering is demonstrated. The out-coupling efficiency and the emission rate are increased by embedding the SPS into a micro-cavity. The design of the micro-cavity is based on detailed modeling to optimize its performance. The resulting resonant single-QD diode is driven at a repetition rate of 1 GHz, exhibiting a second-order correlation function of g(2)(0) = 0. Eventually, QDs grown on (111)-oriented substrates are proposed as a source of entangled photon pairs. Intrinsic symmetry-lowering effects leading to the splitting of the exciton bright states are shown to be absent for this substrate orientation. As a result, the XX rarr X rarr 0 recombination cascade of a QD can be used for the generation of entangled photons without further tuning of the fine-structure splitting via QD size and/or shape.

Electronic Properties of Self-Organized Nanostructures: Theoretical Modeling on the Basis of the Scanning Tunneling Microscopy Characterization

An adequate modeling of the self-organized nanostructures is possible only on the basis of the modern characterization of those nanostructures. We discuss the recent results of modeling of self-organized semiconductor quantum dots and quantum rings as well as metal nanoislands based on the Scanning Tunneling Microscopy characterization. The examples given in the present review demonstrate a high level of complexity needed for a theoretical model to adequately represent the specific features of a nanosystem as determined by the Scanning Tunneling Microscopy.

Universal shapes of self-organized semiconductor quantum dots: Striking similarities between InAs∕GaAs(001) and Ge∕Si(001)

The model systems for self-organized quantum dots formed from elemental and compound semiconductors, namely Ge grown on Si(001) and InAs on GaAs(001), are comparatively studied by scanning tunneling microscopy. It is shown that in both material combinations only two well-defined families of faceted and defect-free nanocrystals exist (and coexist). These three-dimensional islands, pyramids, and domes show common morphological characteristics, independent of the specific material system. A universal behavior is further demonstrated in the capping-passivation process that turns the nanocrystals in true quantum dots.

Optical properties of single semiconductor quantum dots

We review the electronic and optical properties of single self-organized semiconductor quantum dots. A particular attention is paid to the description of the fundamental electron/hole levels, which govern the ground state interband transition. We show that a fine description of the fundamental transition goes far beyond a simple atomic-like picture, and that the optical properties of an isolated quantum dot are dependent upon different weak couplings, which reflect its intrinsic solid state nature and should be incorporated in any theoretical scheme aiming at describing its response to light. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of Morphology and Chemical Composition of Self-Organized Semiconductor Quantum Dots and Wires by X-Ray Scattering

X-ray scattering methods suitable for the investigation of the morphology and chemical composition of self-organized quantum dots and quantum wires are reviewed. Their application is demonstrated in experimental examples showing that a combination of small angle X-ray scattering with high-resolution X-ray diffraction can reveal both the shape and the chemical composition of the self-organized objects.

Effect of the quantum-dot surface density in the active region on injection-laser characteristics

A new method of increasing the surface density of self-organized semiconductor quantum dots formed by molecular-beam epitaxy is proposed. A comparative analysis of the characteristics of injection lasers based on quantum-dot arrays with different surface density is made. It is shown that the use of quantum-dot arrays of higher density makes it possible to decrease substantially the threshold current density in the region of large losses and to increase the maximum gain and the maximum output radiation power.