I. V. Shtrom

Dopant-stimulated growth of GaN nanotube-like nanostructures on Si(111) by molecular beam epitaxy

In this paper we study growth of quasi-one-dimensional GaN nanowires (NWs) and nanotube (NT)-like nanostructures on Si(111) substrates covered with a thin AlN layer grown by means of plasma-assisted molecular beam epitaxy. In the first part of our study we investigate the influence of the growth parameters on the geometrical properties of the GaN NW arrays. First, we find that the annealing procedure carried out prior to deposition of the AlN buffer affects the elongation rate and the surface density of the wires. It has been experimentally demonstrated that the NW elongation rate and the surface density drastically depend on the substrate growth temperature, where 800 °C corresponds to the maximum elongation rate of the NWs. In the second part of the study, we introduce a new dopant-stimulated method for GaN nanotube-like nanostructure synthesis using a high-intensity Si flux. Transmission electron microscopy was used to investigate the morphological features of the GaN nanostructures. The synthesized structures have a hexagonal cross-section and possess high crystal quality. We propose a theoretical model of the novel nanostructure formation which includes the role of the dopant Si. Some of the Si-doped samples were studied with the photoluminescence (PL) technique. The analysis of the PL spectra shows that the highest value of donor concentration in the nanostructures exceeds 5∙1019 cm−3.

Anapoles in Free-Standing III–V Nanodisks Enhancing Second-Harmonic Generation

Nonradiating electromagnetic configurations in nanostructures open new horizons for applications due to two essential features: a lack of energy losses and invisibility to the propagating electromagnetic field. Such radiationless configurations form a basis for new types of nanophotonic devices, in which a strong electromagnetic field confinement can be achieved together with lossless interactions between nearby components. In our work, we present a new design of free-standing disk nanoantennas with nonradiating current distributions for the optical near-infrared range. We show a novel approach to creating nanoantennas by slicing III-V nanowires into standing disks using focused ion-beam milling. We experimentally demonstrate the suppression of the far-field radiation and the associated strong enhancement of the second-harmonic generation from the disk nanoantennas. With a theoretical analysis of the electromagnetic field distribution using multipole expansions in both spherical and Cartesian coordinates, we confirm that the demonstrated nonradiating configurations are anapoles. We expect that the presented procedure of designing and producing disk nanoantennas from nanowires becomes one of the standard approaches to fabricating controlled chains of standing nanodisks with different designs and configurations. These chains can be essential building blocks for new types of lasers and sensors with low power consumption.

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.

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.

III-V nanoantennas fabricated from nanowires for enhanced nonlinear optical signal at Mie resonances

In our work, we employ the resonant electromagnetic properties of III-V semiconductor nanowires to design building blocks for nonlinear all-dielectric metamaterials and devices. Contrary to widely used Si and Ge nanostructures, III-V materials, such as GaAs or AlGaAs, have a direct band gap and non-centrosymmetric crystal structure, which makes them promising for the development of nonlinear metamaterials. We developed an innovative approach to fabricate disk and rod nanoantennas by slicing bottom-up grown nanowires using a focused ion beam milling (FIB). The proposed method allows to significantly decrease the influence of the substrate on the electromagnetic field distribution inside the nanoantenna and it opens the possibility to use any substrate regardless of the nanostructure fabrication process. With this technique, we study the influence of geometry, design and crystal structure on the characteristics of all-dielectric nanoantennas. It offers unique opportunities to fabricate high-quality structures with variable radii, longitudinal heterostructures with lattice-mismatched materials, and structures with different refractive indexes and crystal phases that are not available in bulk materials.

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.

MBE growth of thin AlGaAs nanowires with a complex structure on strongly mismatched SiC/Si(111) substrate

The possibility of AlGaAs nanowires MBE growth on a silicon substrate with a nanometer silicon carbide buffer layer was demonstrated for the first time. Under the same experimental conditions (including the same composition), the diameter of the AlGaAs/SiC/Si nanowires are smaller than nanowires diameter grown on a silicon substrate. Based on the photoluminescence analysis suggests that when AlGaAs/SiC/Si NWs are grown, a physical complex structure appears due to the self-organized formation of regions with different molar fractions of aluminum in the solid solution.

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.

INFLUENCE OF HYDROSTATIC PRESSURE ON EXCITON PHOTOLUMINESCENCE SPECTRUM OF EXCITON MOLECULES InAs/GaAs

The influence of hydrostatic pressure in the range 0–12 kbar on exciton photoluminescence spectrum of InAs quantum dot molecules was studied. The molecular terms related luminescence with the increase of excitation density was obtained. For all components baric coefficients were found. Anomalies in baric dependences for p+- and d+- excited molecule states are discussed.