卷 52, 编号 14 (2018)

“We present experimental and theoretical study of the photoluminescence in a set of double asymmetric CdSe/ZnSe quantum wells with self-assembled quantum dots separated by rather thick ZnSe barrier. It is found that for a certain ratio between depths of quantum wells hot exciton channel in the photoluminescence excitation spectrum of shallow well is dominant up to the energy interval exceeding 10 longitudinal optical phonons above the bottom of the exciton zone of the ZnSe. A model of the electrons, holes, and excitons transfer within the system of asymmetric quantum wells is developed. We demonstrate that the prevailing of the exciton channel is due to different rate of transitions between quantum wells of excitons and single charge carriers”.

The possible existence of the bound states of the interacting two-dimensional (2D) magnetoexcitons in the lowest Landau levels (LLLs) approximation was investigated using the Landau gauge description. The magnetoexcitons taking part in the formation of the bound state with resultant wave vector \({\mathbf{k}} = 0\) have opposite in-plane wave vectors \({\mathbf{k}}\) and \( - {\mathbf{k}}\) and look as two electric dipoles with the arms oriented in-plane perpendicularly to the corresponding wave vectors. The bound state of two antiparallel dipoles moving with equal probability in any direction of the plane with equal but antiparallel wave vectors is characterized by the variational wave function of the relative motion \({{\varphi }_{n}}({\mathbf{k}})\) depending on the modulus \({\text{|}}{\mathbf{k}}{\text{|}}\). The spins of two electrons and the effective spins of two holes forming the bound states were combined separately in the symmetric or in the antisymmetric forms \(( \uparrow \downarrow \, + \eta \, \downarrow \uparrow )\) with the same parameter \(\eta = \pm 1\) for electrons and holes. In the case of the variational wave function \({{\varphi }_{2}}(k) = {{(8{{\alpha }^{3}})}^{{1/2}}}{{k}^{2}}l_{0}^{2}\exp [ - \alpha {{k}^{2}}l_{0}^{2}]\) the maximum density of the magnetoexcitons in the momentum space representation is concentrated on the in-plane ring with the radius \({{k}_{r}} = 1{\text{/}}(\sqrt \alpha {{l}_{0}}).\) The stable bound states of the bimagnetoexciton molecule do not exist for both spin orientations. Instead of them, a deep metastable bound state with the activation barrier comparable with the ionization potential \({{I}_{l}}\) of the magnetoexciton with \({\mathbf{k}} = 0\) was revealed in the case \(\eta = 1\) and \(\alpha = 0.5\). In the case \(\eta = - 1\) and \(\alpha = 3.4\) only a shallow metastable bound state can appear.

Nowadays modern science and technology require development of efficient electromagnetic emitters covering far GHz and THz ranges. Semiconductor elements with negative differential resistance (NDR) such as Gunn diodes based on GaAs and InP are well-established powerful microwave emitters. In this work the Gunn diode structure based on single GaN nanowire with the potential of THz device development was proposed and investigated both theoretically and experimentally. According to the results of the numerical modeling, the Gunn generation can be obtained in the proposed geometry. Dependence of the doping concentration on the NW length necessary for the electrons domain formation was obtained. The nanostructures were grown via molecular beam epitaxy technique. Contacts to single nanowires were fabricated with the combination of e-beam lithography and thermal evaporation. It was shown experimentally that the volt-ampere characteristics of the GaN nanowire structure possess current saturation region. Experimental results correspond well to proposed numerical model.

The object of the investigation was n-type mercury chalcogenide (Mn_0.11Hg_0.89Te) monocrystal which was grown by crystallization from a two-phase mixture with replenishment of the melt from a tellurium solution. The investigations of microwave absorption derivative (dP/dH) showed the existence of strong high and low frequency oscillations in the magnetic field in the temperature range 4.2–20 K. The concentration and effective mass of charge carrier were determined from oscillation period and temperature dependence of oscillation amplitude.

The dynamically compressed coherent exciton-polariton condensate state was implemented at the low polariton (LP) band bottom in GaAs microcavity resonantly excited in a wide range of wavevectors by the convergent 2.5-ps long Gaussian linearly polarized beam when the active region of the cavity was ahead of the waist. Formation of the dynamically compressed condensate state at the LP band bottom and its further dynamics are shown to be well described by the Gross-Pitaevskii equation. The state persists for several picosecond until LP-LP repulsion causes its expansion in both spatial and momentum spaces. Dynamic compression of an elliptically polarized LP system is found to occur without preserving its initial polarization: the dynamic compression of weakly interacting components with σ⁺ and σ⁻ polarization occurs almost independently.

A label-free high-performance electrochemical sensing of single nucleotide polymorphism in native genomic DNA samples from cancer tissues, in oncogene-specific complementary DNA and in amplicons has been carried out on bundles of few-walled carboxylated carbon nanotubes, surface of which was coated with electron-dense layer of probe DNA. High selectivity and sensitivity of the novel DNA-nanosensor are ensured by the following features. Firstly, a complementary-hybridization signal is enhanced by resonance between plasmons in carbon nanotubes and dipole oscillations of hydrated nucleic acids located in near-electrode Helmholtz double layer of the impedance sensor. Secondly, a decoration of carbon nanotubes by adhered metal atoms in a high-spin state leads to Fermi level stabilization for the carbon nanotube bundles.

InAlN/AlN/GaN semiconductor heterostructures with a barrier thickness of 5–13 nm have been grown by metalorganic vapor phase epitaxy (MOVPE) on sapphire and SiC substrates. Optimization of GaN buffer and InAlN layers allows fabricating structures with sheet conductivity values below 210 Ohm/sq. High electron mobility transistors (HEMTs) fabricated from such structures show drain current value exceeding 1.25 A/mm with maximum transconductance of 450 mS/mm. Use of thin in situ Si₃N₄ capping allows to fabricate and compare HEMT and MIS-HEMTs.

We have investigated spectral and spectral-kinetic properties of hybrid (organic semiconductor-plasmonic metal) nanocomposites on the base of silver nanoparticle monolayers and thin nickel phthalocyanine (NiPc) films. The spectroscopic results obtained by the femtosecond pump-probe technique demonstrate an enhancement of the fast optical response in the range of long-wavelength NiPc electronic absorption bands when the NiPc thin films contact with silver nanoparticles. This could be assigned to the plasmon-related modification and the enhancement of hybrid structures absorption at its steady-state absorption spectra.

We have investigated Tamm plasmon structure and periodic metal-dielectric structures with active organic CBP (N,N-dicarbazolyl-4,4-biphenyl) layer. Tamm structure is based on SiO₂/TiO₂ 5 pairs DBR, with 26 nm CBP and 50 nm silver layer on the top of it. Two periodic silver-organic structures using thermal evaporation technique with different CBP layer thickness (15 and 30 nm) was fabricated. The rate of fluorescence intensity decay of Tamm plasmon and periodic structures was experimentally measured in near ultraviolet region. We demonstrate, that decay time of CBP fluorescence intensity in Tamm plasmon structure and periodic metal-organic structures decreases several times.

Two-dimensional (2D) semiconductor structures of materials without inversion center (e.g. zinc-blende A^IIIB^V) possess the zero-field conduction band spin-splitting (Dresselhaus term), which is linear and cubic in wavevector k, that arises from cubic in k splitting in bulk material. At low carrier concentration the cubic term is usually negligible. However, if we will be interested in the following dimensional quantization (in 2D plane) and the character width in this direction is comparable with the width of 2D-structure, then we have to take into account k³-terms as well (even at low concentrations), that after quantization leads to comparable contribution that arises from k-linear term. We propose the general procedure for derivation of Dresselhaus spin-splitting Hamiltonian applicable for any curvilinear 1D-structures. The simple examples for the cases of quantum wire (QWr) and quantum ring (QR) defined in usual [001]-grown 2D-structure are presented.

CMOS and SOI technology compatible structures and devices are currently intensively investigated by many research groups, since various effects observed in such structures can be relatively easy implemented in electronic devices thereby expanding their functionality. The most promising is the research and development of spintronic devices, which will allow using both electron charge and spin degrees of freedom for transmission, storage and processing of information. In this work we report the fabrication process of 3-terminal (3-T) ferromagnet/silicon devices of two types. First is the planar Fe₃Si/Si 3-T structure with 5 μm gap between closest ferromagnetic electrodes. Second is silicon nanowire back-gate transistor with Fe film source and drain synthesized on SOI substrate. Transport and magnetotransport properties of both devices are investigated.

The structural and electronic characteristics of epitaxial graphene films grown by thermal decomposition of the Si face of a semi-insulating 4H-SiC substrate in an argon environment have been studied by a large set of analytical techniques. It is shown that the results of a complex study make it possible to optimize the growth parameters and develop a reliable technology for the growth of high-quality single-layer graphene films. The charge-carrier concentration in the graphene layer was within 7 × 10¹¹–1 × 10¹² cm^–2, and the maximum mobility of electrons at room temperature approached 6000 cm²/(V s).

Using a combination of the density functional theory and tight-binding calculations, we study electronic and optical properties of asymmetric chevron-type graphene nanoribbons recently synthesized with atomic precision. We demonstrate that the low-energy optical selection rules in such infinite chiral ribbons are more reminiscent of those for zigzag rather than for armchair ribbons. It is also shown that, starting from about 25 nm long ribbons, the low-energy absorption and therefore the selection rules of infinitely long ribbons are well reproduced in the finite cluster approach. Hence, ribbons longer than 25 nm (about 28 unit cells) can be treated as infinitely long ones.

We present results of experiments concerning the loss of internal quantum efficiency of the GaAs/AlGaAs heterostructure due to the focused ion beam-induced radiation defects. Firstly we show that 300°C annealing in the high vacuum conditions leads to a partial recovery of the internal quantum efficiency and, therefore, photoluminescence regains some of its intensity. Secondly we show that 620°C annealing in the presence of As vapor leads up to 80% recovery of the internal quantum efficiency depending on the etching depth. Achieved results proves focused ion beam technique to be potent for the fabrication of photonic structures based on A3B5 materials containing active layer.

A search for materials suitable for implementation of 1.55 µm Al-free diode lasers based on InP with asymmetric barrier (AB) layers is conducted. It is shown that a very high (over 10⁶) suppression ratio of the parasitic electron flux can be achieved using common III–V alloys for the ABs. Hence placing such ABs in the immediate vicinity of the active region should completely suppress the parasitic recombination in the waveguide. Several optimal AB designs are proposed that are based on one of the following alloys: Al-free GaInPSb, ternary AlInAs, or quaternary AlGaInAs with a low Al-content. As an important and beneficial byproduct of utilization of such ABs, an improvement of majority carrier capture into the active region occurs.