Quantum Wire Dot Research Articles

Erratum: “Nonlinear organic plasmonics: Applications to optical control of Coulomb blocking in nanojunctions” [Appl. Phys. Lett. 107, 053302 (2015)

Purely organic materials with negative and near-zero dielectric permittivity can be easily fabricated. Here we develop a theory of nonlinear non-steady-state organic plasmonics with strong laser pulses. The bistability response of the electron-vibrational model of organic materials in the condensed phase has been demonstrated. Non-steady-state organic plasmonics enable us to obtain near-zero dielectric permittivity during a short time. We have proposed to use non-steady-state organic plasmonics for the enhancement of intersite dipolar energy-transfer interaction in the quantum dot wire that influences on electron transport through nanojunctions. Such interactions can compensate Coulomb repulsions for particular conditions. We propose the exciton control of Coulomb blocking in the quantum dot wire based on the non-steady-state near-zero dielectric permittivity of the organic host medium.

Nonlinear organic plasmonics: Applications to optical control of Coulomb blocking in nanojunctions

Purely organic materials with negative and near-zero dielectric permittivity can be easily fabricated. Here, we develop a theory of nonlinear non-steady-state organic plasmonics with strong laser pulses that enable us to obtain near-zero dielectric permittivity during a short time. Our consideration is based on the model of the interaction of strong (phase modulated) laser pulse with organic molecules developed by one of the authors before, extended to the dipole-dipole intermolecular interactions in the condensed matter. We have proposed to use non-steady-state organic plasmonics for the enhancement of intersite dipolar energy-transfer interaction in the quantum dot wire that influences on electron transport through nanojunctions. Such interactions can compensate Coulomb repulsions for particular conditions. We propose the exciton control of Coulomb blocking in the quantum dot wire based on the non-steady-state near-zero dielectric permittivity of the organic host medium.

Modeling of quantum dot junction for third generation solar cell

To improve efficiency, third generation solar cells shall include quantum nanostructures. We developed numerical calculations within the Keldysh formalism to investigate the photovoltaic properties of a quantum wire–dot–wire concept cell. A photocurrent is produced at zero bias voltage for a very narrow range of photon energy. We moreover explain how the spectral current densities show a single peak response close to the resonance while a double peak one far from it.

Thermal escape and capture processes in quantum wire–dot structures

We study the dynamics of an electronic wave packet in a quantum wire with an embedded quantum dot interacting with an LO-phonon bath at room temperature. Two different cases are studied: in the first scenario (escape scenario), we determine the probability for the electrons to leave the dot by absorption of an LO-phonon. In the second scenario (capture and escape scenario), we study the capture process from the delocalized states of the wire into the localized states of the dot accompanied by re-emission into the delocalized states. These scenarios are analysed by using a quantum kinetic theory for the electron LO-phonon interaction. The thermal escape scenario shows a continuous flow of density directed with equal probabilities to both sides from the dot accompanied by small oscillations in the density of bound carriers. For the capture and escape scenario, we find an interplay between thermal escape and a coherent escape process, the latter being present even at zero temperature. In the coherent escape, a part of the captured density re-escapes and forms additional travelling wave packets following the original wave packet.

Molecular beam epitaxy of quantum wires and quantum dots on patterned high-index substrates

Using a novel growth mechanism on patterned high-index GaAs (311)A substrates we have developed a new concept to fabricate quantum wires and quantum dots as well as coupled quantum wire–dot arrays by molecular beam epitaxy. The combination of self-organized growth with lithographic patterning and the assistance of atomic hydrogen produces these quasi-planar lateral nanostructure arrays with unprecedented uniformity in size and composition and with controlled positioning on the wafer. The sought for one- and zero-dimensional nature of these quantum wire and quantum dot arrays manifests itself in the superior optical properties. To functionalize our lateral semiconductor quantum wire and quantum dot arrays with the properties of magnetic thin films, epitaxial Fe layers have been grown on GaAs (311)A. Defect free Fe layers are obtained on As-saturated GaAs surfaces. The large electrical conductivity of thin Fe layers indicates reduced Fe–GaAs interface compound formation. An unusual in-plane spontaneous Hall-effect is observed in these epitaxial Fe layers of reduced symmetry.

Near-field optical imaging and spectroscopy of a coupled quantum wire-dot structure

A coupled GaAs/AlGaAs quantum wire (QWR)-dot sample grown by molecular beam epitaxy on a patterned $(311)A$ GaAs substrate is studied by near-field spectroscopy at a temperature of 10 K with a spectral resolution of 100 \ensuremath{\mu}eV. The two-dimensional potential energy profiles of the sample including localized excitonic states caused by structural disorder are determined in photoluminescence measurements with a spatial resolution of 150 nm. One finds a potential barrier of 20 meV between the quantum wire and the embedding quantum well (QW) on the mesa top of the structure. This is due to local thinning of the GaAs layer. In contrast, the wire-dot interface results free of energy barriers. The spatial variation of the GaAs layer thickness provides information on the growth mechanism determined by lateral diffusion of Ga atoms which is modeled by an analytical model. By performing spatially resolved photoluminescence excitation measurements on this wire-dot structure, we present a method for investigating carrier transport in low-dimensional systems: The dot area is used as an optical marker for excitonic diffusion via QW and QWR states. The two-dimensional (2D) and 1D diffusion coefficients are extracted as a function of the temperature and discussed.

Realization of InP-Based InGaAs single electron transistors on wires and dots grown by selective MBE

InGaAs quantum wires (QWRs) and InGaAs quantum wire-dot coupled structures were formed by selective MBE growth on patterned InP substrates, and attempts were made to realize single-electron transistors (SETs) on them. Investigation of basic optical and transport characteristics of both nanostructures by PL, CL and magnetotransport measurements revealed realization of high quality quantum nanostructures. In the coupled structure, double barrier potential profile essential for SET was realized in a self-organizing fashion without any additional processing. The SETs made on wires showed clear Coulomb oscillations up to 30 K, indicating realization of small quantum dots (QDs) and high potential barriers by this approach.

Selective molecular beam epitaxy growth of quantum wire–dot coupled structures with novel high index facets for InGaAs single electron transistor arrays

For the InGaAs wire–dot–wire coupled structure arrays formed by selective molecular beam epitaxy (MBE) growth method on a specially designed patterned InP substrates, applicability to high density InGaAs single electron transistor (SET) arrays were investigated from the viewpoint of reproducibility of the selective MBE growth, size controllability and integration level. Appearance of the crater-like structure becomes a problem for reproducible formation of the InGaAs quantum wire–dot coupled structure. However, such a crater structure can be removed by appropriately adjusting growth condition and pattern sizes. The InGaAs wire size, the InGaAs dot size and the lateral width of the potential barrier were found to be controlled by the growth condition and the pattern geometry and can be reduced down to decananometer range. Highly integrated SET circuits with the device density larger than 109cm−2 appear to be realizable using the present selective MBE method.

Control of Dot Size and Tunneling Barrier Profile in In0.53Ga0.47As Coupled Quantum Wire-Dot Structures Grown by Selective Molecular Beam Epitaxy on Patterned InP Substrates

Efforts were made to control the dot size and tunneling barrier profiles in In0.53Ga0.47As coupled quantum wire-dot-wire structures formed by selective molecular beam epitaxial (MBE) growth on patterned InP substrates. According to detailed investigation using a scanning electron microscope (SEM), atomic force microscope (AFM) and cathodoluminescence (CL) spectroscopy, the size of the quantum dot and the lateral width of the potential barrier can be controlled by suitably selecting growth conditions and pattern geometry. A minimum dot width and lateral barrier width of about 100 nm and 80 nm, respectively, were achieved in a controlled fashion, indicating applicability of the present approach to direct formation of single-electron transistor (SET) arrays.

Direct formation of InGaAs coupled quantum wire–dot structures by selective molecular beam epitaxy on InP patterned substrates

A new approach to grow an array of InGaAs coupled quantum wire–dot structures by a single growth run of selective MBE on a specially patterned InP substrate is presented. A detailed CL study revealed successful formation of an array of high quality InGaAs coupled wire–dot structures having a double barrier potential profile between the wires and the dot. The present structure may be useful for fabrication of single electron device arrays.