A M Mozharov

Tuning of Magnetic Optical Response in a Dielectric Nanoparticle by Ultrafast Photoexcitation of Dense Electron-Hole Plasma.

We propose a novel approach for efficient tuning of optical properties of a high refractive index subwavelength nanoparticle with a magnetic Mie-type resonance by means of femtosecond laser irradiation. This concept is based on ultrafast photoinjection of dense (>10(20) cm(-3)) electron-hole plasma within such nanoparticle, drastically changing its transient dielectric permittivity. This allows manipulation by both electric and magnetic nanoparticle responses, resulting in dramatic changes of its scattering diagram and scattering cross section. We experimentally demonstrate 20% tuning of reflectance of a single silicon nanoparticle by femtosecond laser pulses with wavelength in the vicinity of the magnetic dipole resonance. Such a single-particle nanodevice enables designing of fast and ultracompact optical switchers and modulators.

Single-stage fabrication of low-loss dielectric nanoresonators from high-loss material

High refractive index subwavelength dielectric nanoresonators, which support both electric and magnetic optical resonances, are a promising platform for many nanophotonic applications. However, the resonant properties of the nanoresonators are highly sensitive to defect concentrations. Therefore, to maintain low defect concentrations, it has generally thought inevitable to use crystalline precursor materials for nanoresonator fabrication. Here, we show that it is possible to fabricate crystalline (low-loss) resonant silicon nanoparticles by femtosecond laser ablation from amorphous (high-loss) silicon thin films. The crystallinity of the fabricated nanoparticles is proven by means of Raman spectroscopy and electron transmission microscopy, and their optical resonant properties are studied by means of dark-field optical spectroscopy and discrete-dipole simulations.

Modeling, synthesis and study of highly efficient solar cells based on III-nitride nanowire arrays grown on Si substrates

In this letter we investigate photovoltaic properties of GaN nanowires (NWs) – Si substrate heterostructure obtained by molecular beam epitaxy (MBE). Antireflection properties of the NW array were studied theoretically and experimentally to show an order of magnitude enhancement in antireflection comparing to the pure Si surface (2.5% vs. 33.8%). In order to determine optimal morphology and doping levels of the structure with maximum possible efficiency we simulated its properties using a finite difference method. The carried out simulation showed that a maximum efficiency should be 20%.

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.

Modeling the semiconductor devices with negative differential resistance based on nitride nanowires

We proposed a numerical model of the Gunn diode and resonant diode based on a single nitride nanowire. Important model parameters needed for development of the considered devices, namely layers thickness, composition and doping level were evaluated. It has been shown theoretically that the single GaN nanowire based Gunn diode is capable to operate in over 1 THz frequency regime.

Core-Shell III-Nitride Nanowire Heterostructure: Negative Differential Resistance and Device Application Potential

In this work we have studied volt-ampere characteristics of single core-shell GaN/InGaN/GaN nanowire. It was experimentally shown that negative differential resistance effect can be obtained in the studied heterostructure. On the base of numerical calculation results the model describing negative differential resistance phenomenon was proposed. We assume this effect to be related with strong localization of current flow inside the nanowire and emergence of Gunn effect in this area.

Droplet epitaxy mediated growth of GaN nanostructures on Si (111) via plasma-assisted molecular beam epitaxy

In this report, we demonstrate that the use of a GaN seeding layer prepared by droplet epitaxy prior to the growth of epitaxial GaN on Si (111) can lead to the formation of oriented arrays of Y-shaped nanoislands (nanotripods) and nanowires and affects the surface density of the nanostructures. From the transmission electron microscopy studies, it is shown that at least some of the seeding islands have a cubic zinc-blende (ZB) GaN structure, and their {111} facets act as the nucleation centers for further growth of GaN nanorods with a wurtzite (WZ) structure. It is also demonstrated that even if the Ga droplets are deposited on the silicon surface prior to the nitridation, a silicon nitride interlayer between silicon and GaN will be inevitably formed in the further growth process. The density and the position of the seeding centers can be controlled with growth parameter variation during the droplet epitaxy; thus the technique proposed and studied in this report can be used for the preparation of site- and density-controlled arrays of nanostructures.

Researching the electrical properties of single A3B5 nanowires

We investigate electrical characteristics of GaN, GaAs and GaP NWs which are grown with MOCVD and MBE. We developed measurement technique and it allows to determine the required properties of the structures.

Study of electrical properties of single GaN nanowires grown by MOCVD with a Ti mask

We researched electrical characteristics of GaN nanowires (NWs) grown by MOCVD through solid titanium film. The technology of creating the ohmic contacts and MESFET structure on single NWs has been developed. The optimal annealing temperature of contacts has been found and conductivity structure, the free carrier concentration and mobility has been evaluated.

Synthesis of GaN nanowires on Si (111) substrates by molecular beam epitaxy

In this work we study growth of semiconductor GaN nanowires (NWs) on Si(111) substrates by means of molecular beam epitaxy. We demonstrate that the substrate temperature affects both the surface density and growth rate of the synthesized NWs. It was determined that at a fixed flux of nitrogen equal to 1.3 cm3/min the maximum growth rate of NWs is ~ 38 nm/h at a substrate temperature — 800 oC. It was also found that the growth rate of NWs on the substrates treated with the oxide removal procedure is half the growth rate on substrates covered with oxide, while their surface density is twice higher in the first case. In addition we have studied influence of Ga flux on NWs formation.