The influence of growth regimes of the silicon capping layer on the optical properties of heterostructures with submonolayer InAs quantum dots embedded in a silicon matrix has been studied. The photoluminescence signal at 1650 nm from submonolayer quantum dots at low temperatures up to 120 K was obtained. It was established that the use of a two-stage method of silicon overgrowing InAs nanoislands makes it possible to increase the photoluminescence intensity by improving the crystalline quality of heterostructures. Analysis of the temperature dependence allowed us to calculate an activation energy for electrons confined in the quantum dots potential well at the level of the thermal energy at room temperature.

Experimental results of studying the InAs islands formation of silicon surface by molecular beam epitaxy are presented. It has been found that, InAs islands with both bimodal and uniform size distributions can be formed depending on the Si surface relief and the presence of nanopits. The possibility of fabricating heterostructures with InAs quantum dots demonstrating photoluminescence in the region of 1.65 μm, was showed.

The self-assembled InAs quantum dots (QDs) in silicon were fabricated by solid source molecular beam epitaxy on $\mathrm{Si}(\mathbf{1 0 0}) 4^{\circ}$ substrates using Wolmer-Veber growth mode. The PL spectra exhibit $1.6 \mu \mathrm{m}$ emission from InAs quantum dots at 10 K. The size-depended luminescence behavior of QDs was observed. As the InAs coverage decreased from 2 to 0.5 monolayers (ML), the photoluminescence peak shifted from 1620 to 1580 nm and increased monotonously.

Experimental results of studying the InAs islands formation of silicon surface by molecular beam epitaxy are presented. It has been found that, InAs islands with both bimodal and uniform size distributions can be formed depending on the Si surface relief and the presence of nanopits. The possibility of fabricating heterostructures with InAs quantum dots demonstrating photoluminescence in the region of 1.65 μm, was showed.

The optical properties of Cu2O nanowhiskers grown by the liquid method with material deposition in an electric field have been studied. The spectral lines forbidden by the selection rules for perfect Cu2O crystals were found in the Raman spectra. The nature of related phonon states is analyzed. In the photoluminescence spectra in the red and near-IR regions, broad bands of defective origin are observed. It was found that the presence of a band at 650 nm (1.9 eV) is a specific feature of the photoluminescence of nanowhiskers. Its properties are studied and possible radiation mechanisms are discussed. In the intrinsic absorption region of nanowhiskers, the photoluminescence band at 572 nm (2.17 eV) associated with band-band transitions is detected. At a low excitation level, the emission of a free exciton n = 1 of the yellow exciton series is observed with simultaneous emission of an optical phonon.

Fabrication of nanocomposite materials consisting of III-V quantum dots (QDs) embedded in silicon (Si) sustained special attention over years. In this work, we present the formation of InAs QD in Si matrix by molecular beam epitaxy and the study of optical properties.

The fabrication of composite material with embedded III-V quantum dots is of great interest due to promising silicon-based light emitting devices. In this work, the growth of self-assembled InAs quantum dots on Si substrates as well as subsequent capping layer for-mation by molecular beam epitaxy is presented. The evolution of size, density and shape of QDs are characterized by atomic-force microscopy. Bimodal size distribution of QDs at the submonolayer InAs coverage was observed. Full embedding into silicon matrix and dislocation free crystal structure of InAs QDs were confirmed by transmission electronic microscopy.

The optical properties of Cu2O nanowhiskers grown by the liquid method with material deposition in an electric field have been studied. The spectral lines forbidden by the selection rules for perfect Cu2O crystals were found in the Raman spectra. The nature of related phonon states is analyzed. In the photoluminescence spectra in the red and near-IR regions, broad bands of defective origin are observed. It was found that the presence of a band at 650 nm (1.9 eV) is a specific feature of the photoluminescence of nanowhiskers. Its properties are studied and possible radiation mechanisms are discussed. In the intrinsic absorption region of nanowhiskers, the photoluminescence band at 572 nm (2.17 eV) associated with band−band transitions is detected. At a low excitation level, the emission of a free exciton n = 1 of the yellow exciton series is observed with simultaneous emission of an optical phonon.

We report a novel mechanism that allows the incorporation of Si into GaN nanowires up to and beyond the solubility limit. This mechanism is documented during the growth on vicinal (misoriented) SiC/Si hybrid substrates having the step bunches. Nanowires that are grown at these locations become heavily Si doped. Such high Si concentrations were verified by secondary-ion mass spectrometry. Photoluminescence data also point to very high carrier concentrations. Moreover, Raman spectroscopy together with quantum chemical modelling shows the build up of Si into Ga sites and indicates even the possibility of the formation of a Ga(Si)N solid solution. The microscopic mechanism responsible for heavy doping and even alloying is diffusion driven by the mechano-chemical effect, which allows for the extremely efficient injection of Si atoms into the nanowires from the step bunches at the vicinal SiC/Si substrates.

The development of a fast semiconductor laser is required for the realization of next-generation telecommunication applications. Since lasers operating on quantum dot ground state transitions exhibit only limited gain due to the saturation effect, we investigate lasing from excited states and compare its corresponding static and dynamic behavior to the one from the ground state. InAs quantum dots (QDs) grown in dot-in-well (DWELL) structures allowed to obtain light emission from ground and three excited states in a spectral range of 1.0–1.3 μ m. This emission was coupled to whispering gallery modes (WGMs) of a 6 μ m microdisk resonator and studied at room temperature by steady-state and time-resolved micro-photoluminescence. We demonstrate a cascade development of lasing arising from the ladder of quantum dot states, and compare the lasing behavior of ground and excited state emission. While the lasing threshold is being increased from the ground state to the highest excited state, the dynamic behavior is improved: turn-on times and lifetimes of WGMs become shorter paving the way towards high frequency direct driven microlasers.

In this work the possibility of thick GaN layers growth by molecular epitaxy on a silicon substrate with nanoscale buffer layer of silicon carbide without any AlN buffer layers was demonstrated for the first time. Morphological and optical properties of the resulting structure are described.

The kinetics of near-edge photoluminescence (PL) in ZnO nanofilms prepared by the atomic layer deposition has been investigated. It is established that the kinetics of near-edge PL in 4-nm films is determined to a great extent by surface 2D-exciton (SX) and biexciton (SXX) complexes. The contribution from surface biexcitons is estimated based on a photostimulated change in the surface potential in ZnO films with different thicknesses. Ultrafast dynamics of surface biexcitons in thin films are revealed. It is shown that biexcitons localized near the surface have the shortest radiative lifetime (less than 100 ps) among all bound exciton complexes, which is explained by the large oscillator strength.

AbstractThe kinetics of near-edge photoluminescence (PL) in ZnO nanofilms prepared by the atomic layer deposition has been investigated. It is established that the kinetics of near-edge PL in 4-nm films is determined to a great extent by surface 2D-exciton (SX) and biexciton (SXX) complexes. The contribution from surface biexcitons is estimated based on a photostimulated change in the surface potential in ZnO films with different thicknesses. Ultrafast dynamics of surface biexcitons in thin films are revealed. It is shown that biexcitons localized near the surface have the shortest radiative lifetime (less than 100 ps) among all bound exciton complexes, which is explained by the large oscillator strength.

Embedding Ge-quantum dot emitters in Mie resonators leads to an enhancement of their luminescence efficiency due to the Purcell effect. To increase this effect, collective Mie resonances in extended Mie-resonator chains are investigated leading to a partial cancellation of radiation losses and experimentally observed Q-factors of up to 500. The corresponding modes and their field localization are theoretically analysed and traced back to a combination of individual oscillating dipoles.

CMOS-compatible light emitters are intensely investigated for integrated active silicon photonic circuits. One of the approaches to achieve on-chip light emitters is the epitaxial growth of Ge(Si) QDs on silicon. Their broad emission in 1.3-1.5 um range is attractive for the telecomm applications. We investigate optical properties of Ge(Si) QD multilayers, that are grown in a thin Si slab on a SOI wafer, by steady-state and time-resolved micro-photoluminescence. We identify Auger recombination as the governing mechanism of carrier dynamics in such heterostructures. Then we demonstrate the possibility of light manipulation at the nanoscale by resonant nanostructures investigating Si nanodisks with embedded Ge(Si) QDs. We show that the Mie resonances of the disks govern the enhancement of the photoluminescent signal from the embedded QDs due to a good spatial overlap of the emitter position with the electric field of Mie modes. Furthermore, we engineer collective Mie-resonances in a nanodisk trimer resulting in an increased Q-factor and an up to 10-fold enhancement of the luminescent signal due to the excitation of anti-symmetric magnetic and electric dipole modes. Using time-resolved measurements we show that the minima of the radiative lifetime coincide with the positions of the Mie resonances for a large variation of disk sizes confirming the impact of the Purcell effect on QD emission rate. Purcell factors at the different Mie-resonances are determined.

Проведены исследования направленности излучения самокаталитических нитевидных нанокристаллов (ННК) типа ННК GaAs в оболочке AlGaAs, полученных методом молекулярно-пучковой эпитаксии с разной степенью легирования бериллием. Показано, что нелегированный образец обладает выраженными волноводными свойствами вдоль направления роста. При увеличении степени легирования возрастает интенсивность излучения, направленного перпендикулярно боковым стенкам ННК. DOI: 10.21883/PJTF.2017.17.44949.16504

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 spontaneous-emission spectra in the near-IR range (0.8–1.3 μm) from inverted tunnel-injection nanostructures are measured. These structures contain an InAs quantum-dot layer and an InGaAs quantum-well layer, separated by GaAs barrier spacer whose thickness varies in the range 3–9 nm. The temperature dependence of this emission in the range 5–295 K is investigated, both for optical excitation (photoluminescence) and for current injection in p–n junction (electroluminescence). At room temperature, current pumping proves more effective for inverted tunnel-injection nanostructures with a thin barrier (<6 nm), when the apexes of the quantum dots connect with the quantum well by narrow InGaAs straps (nanobridges). In that case, the quenching of the electroluminescence by heating from 5 to 295 K is slight. The quenching factor S T of the integrated intensity I is S T = I 5/I 295 ≈ 3. The temperature stability of the emission from inverted tunnel-injection nanostructures is discussed on the basis of extended Arrhenius analysis.

Ex post manipulation of ∼1.1 μm emitting InGaAs/GaAs-based quantum dot–quantum well tunnel injection light emitting devices is demonstrated experimentally. The devices were operated at elevated forward currents until irreversible alterations were observed. As a result, changes in the steady-state optical spectra (electroluminescence, photoluminescence, and photocurrent), in carrier kinetics, in transport properties, and real structure are found. Except for degradation effects, e.g., of larger quantum dots, also restoration/annealing effects such as increased tunnel barriers are observed. The results furnish evidence for a generic degradation mode of nanostructures. We qualitatively interpret the mechanisms involved on both the nanoscopic and the device scales.

We report on Sn-contained nanocrystals formed in Si and SiGe matrixes via Sn precipitation upon annealing of thin metastable Si1−x−yGexSny layers grown by molecular beam epitaxy. The nanocrystals exhibit a cubic lattice, which is coherent with the matrix. The density of the nanocrystals decreases with the annealing temperature revealing a kinetic formation pathway. New optical spectral features below the Si band gap are observed in photoluminescence spectra of the samples with nanocrystals. The origin of these new spectral features is discussed.