A. I. Khrebtov

Composite system based on CdSe/ZnS quantum dots and GaAs nanowires

The possibility of fabricating a composite system based on colloidal CdSe/ZnS quantum dots and GaAs nanowires is demonstrated and the structural and emission properties of this system are investigated by electron microscopy and photoluminescence spectroscopy techniques. The good wettability and developed surface of the nanowire array lead to an increase in the surface density of quantum dots and, as a consequence, in the luminosity of the system in the 600-nm wavelength region. The photoluminescence spectrum of the quantum dots exhibits good temperature stability in the entire range 10–295 K. The impact of surface states on energy relaxation and the role of exciton states in radiative recombination in the quantum dots are discussed.

Hybrid AlGaAs/GaAs/AlGaAs nanowires with a quantum dot grown by molecular beam epitaxy on silicon

Data on the growth features and physical properties of GaAs inserts embedded in AlGaAs nanowires grown on Si(111) substrates by Au-assisted molecular beam epitaxy are presented. It is shown that by varying the growth parameters it is possible to form structures like quantum dots emitting in a wide wavelength range for both active and barrier regions. The technology proposed opens up new possibilities for the integration of direct-band III–V materials on silicon.

Specific features of resonant nonlinear absorption in colloidal solutions of CdSe/ZnS quantum dots

Nonlinear refraction coefficients and nonlinear absorption coefficients of colloidal solutions of CdSe/ZnS quantum dots (QDs) have been measured by the z-scan method. Resonant excitation was carried out by a Nd:YAG laser (λ = 532 nm, τ ∼ 7 ns). QDs have been chosen to correspond to different positions of the peak of the fundamental exciton absorption band with respect to the laser wavelength. The z-scan data are compared with the optical-limitation photodynamics data on CdSe/ZnS QD solutions. The obtained values of nonlinear absorption coefficients and their dependence on the QD size are interpreted in terms of the two-step mechanism of optical limitation.

The effect of external gaseous environments on the photoluminescence intensity of quantum-dimensional composite system

The luminescence properties of the composite system based on colloidal CdSe/ZnS core shell quantum dots and GaAs nanowires under continuous laser irradiation are investigated. The phenomenon of photoinduced luminescence enhancement under various gaseous environments is shown. In addition to the previously reported mechanisms of the photoluminescence enhancement, a new one which is connected to the quantum dots losses of vibrational energy during the collisions with molecules of external gases is proposed.

A hybrid system of GaAs whisker nanocrystals and PbS quantum dots on silicon substrate

It is shown that a hybrid nanocomposite structure can be created by integration of semiconducting materials with different dimensionalities: an array of quasi-1D GaAs whisker nanocrystals formed by molecular-beam epitaxy on a Si (111) substrate and 0D PbS colloidal quantum dots. The morphological and spectral properties of the resulting system are analyzed.

Study of the electrical properties of individual (Ga,Mn)As nanowires

Arrays of (Ga, Mn)As nanowire crystals are synthesized by molecular-beam epitaxy. Electronbeam lithography made possible the fabrication of electric contacts to individual nanowires. The influence of the annealing temperature on the properties of the contacts is studied. The optical annealing temperature is determined to be 160°C. It is found that an increase in the annealing temperature yields structure degradation. From studies of the current-voltage characteristics of the individual nanowire structures, a number of their electrical parameters, such as the resistivity and the mobility of charge carriers are determined.

Hybrid GaAs/AlGaAs Nanowire—Quantum dot System for Single Photon Sources

III–V nanowires, or a combination of the nanowires with quantum dots, are promising building blocks for future optoelectronic devices, in particular, single-photon emitters, lasers and photodetectors. In this work we present results of molecular beam epitaxial growth of combined nanostructures containing GaAs quantum dots inside AlGaAs nanowires on a silicon substrate showing a new way to combine quantum devices with Si technology.

Nanowire Quantum Dots Tuned to Atomic Resonances

Quantum dots tuned to atomic resonances represent an emerging field of hybrid quantum systems where the advantages of quantum dots and natural atoms can be combined. Embedding quantum dots in nanowires boosts these systems with a set of powerful possibilities, such as precise positioning of the emitters, excellent photon extraction efficiency and direct electrical contacting of quantum dots. Notably, nanowire structures can be grown on silicon substrates, allowing for a straightforward integration with silicon-based photonic devices. In this work we show controlled growth of nanowire-quantum-dot structures on silicon, frequency tuned to atomic transitions. We grow GaAs quantum dots in AlGaAs nanowires with a nearly pure crystal structure and excellent optical properties. We precisely control the dimensions of quantum dots and their position inside nanowires and demonstrate that the emission wavelength can be engineered over the range of at least 30 nm around 765 nm. By applying an external magnetic field, we are able to fine-tune the emission frequency of our nanowire quantum dots to the D2 transition of 87Rb. We use the Rb transitions to precisely measure the actual spectral line width of the photons emitted from a nanowire quantum dot to be 9.4 ± 0.7 μeV, under nonresonant excitation. Our work brings highly desirable functionalities to quantum technologies, enabling, for instance, a realization of a quantum network, based on an arbitrary number of nanowire single-photon sources, all operating at the same frequency of an atomic transition.

Directional emission from beryllium doped GaAs/AlGaAs nanowires

The emission directionality of self-catalytic GaAs nanowires in an AlGaAs shell, produced by molecular-beam epitaxy with a varied level of beryllium doping, is studied. It is shown that an undoped sample possesses pronounced waveguide properties along the growth direction. With increasing doping level, the intensity of the emission directed perpendicular to the lateral nanowire walls grows.

The dependence of the wavelength on MBE growth parameters of GaAs quantum dot in AlGaAs NWs on Si (111) substrate

The data on the growth peculiarities and physical properties of GaAs insertions embedded in AlGaAs nanowires grown on Si (111) substrates by Au-assisted molecular beam epitaxy are presented. It is shown that by varying of the growth parameters it is possible to form structures like quantum dots emitting in a wide wavelengths range for both active and barrier parts. The technology proposed opens new possibilities for the integration of direct-band AIIIBV materials on silicon platform.