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A new method for the formation of three-dimensional quantum-dimensional InGaP(As) islands is proposed, which consists in replacing phosphorus with arsenic in an InGaP layer deposited on GaAs directly during epitaxial growth. It is shown that the replacement of phosphorus with arsenic results in formation of three-dimensional islands in the thin InGaP layer. At room temperature, these islands emit light in the spectral range of 0.95–0.97 µm. The estimated density of the islands is 1.3 × 1010 cm–2. [ABSTRACT FROM AUTHOR]

We have studied heterostructures based on short-period InGaAs/InGaAlAs superlattices (SLs) manufactured by molecular-beam epitaxy on InP substrates, intended for use as active regions in vertical-cavity surface-emitting lasers operating in a 1.3-μm spectral range. The heterostructures were characterized by measuring photoluminescence (PL) emission and X-ray diffraction. It is established that variation of the ratio of quantum-well and barrier-layer thicknesses in the SL allows controlled shift of the PL peak position for lasing in the 1.3-μm range at almost constant PL efficiency. [ABSTRACT FROM AUTHOR]

The properties of multilayer α-Si(Ge)/SiO2 nanostructures deposited onto p-Si substrates and annealed at various temperatures are investigated. The total nanolayer thickness is no larger than 300–350 nm. It is found that despite the formation of crystals in a nanolayer, the quantum-size effect does not manifest itself in the photoelectric properties of the nanolayer–substrate heterojunction in the studied temperature range of 300–900 nm. At the same time, the photocurrent efficiency (A/W) in this range becomes constant. The found results are explained by a small nanolayer thickness. When applying a sufficiently large lock bias, the electric field of the nanolayer–substrate junction reaches the outer nanolayer boundary, which abruptly decreases the surface carrier recombination. Just this recombination usually suppresses the photodetector sensitivity in the short-wavelength spectral region. The constant efficiency of the studied heterostructures in a broad spectral range makes them attractive for use in various photoelectric devices. [ABSTRACT FROM AUTHOR]

InAs and In0.8Ga0.2As quantum dots in a GaAs matrix as well as GaAs solar cells with quantum dots of both types in the i-region are obtained by metalorganic vapor-phase epitaxy. As a result of investigations by photoluminescence and transmission electron microscopy, it is found that the In0.8Ga0.2As quantum-dot array is highly uniform, contains a smaller number of large imperfect quantum dots, and also provides a decrease in mechanical stresses in the structure. An analysis of the spectral dependences of the internal quantum yield shows that the quality of a solar-cell matrix after embedding up to 20 rows of In0.8Ga0.2As quantum dots remains at a level close to the reference GaAs solar cells. In this case, a linear increase in the additional photocurrent generated due to the absorption of sub-bandgap photons in In0.8Ga0.2As quantum dots is provided with an increase in the number of rows of quantum dots, since the value of the photocurrent gain per row is preserved. [ABSTRACT FROM AUTHOR]

In this study, the effect of mechanical activation of coprecipitated hydroxide precursor on synthesis of gadolinium zirconate Gd2Zr2O7 has been studied. Mechanical activation of the precursor has been performed in an AGO-2 laboratory centrifugal-planetary mill at a centrifugal factor of 20 g with zirconia vials and balls. Particular attention has been given to carbonization of the as-prepared and mechanically activated precursors due to reaction with atmospheric carbon dioxide and their decarbonization in the course of calcination. The removal of the volatile components (H2O and CO2) from the as-prepared and mechanically activated precursors can be achieved by calcination at 1100–1200 °C for 3 h. Calcination of the as-prepared and mechanically activated precursors in the range of 700–1200 °C results in the formation of nanocrystalline fluorite-type Gd2Zr2O7. Gadolinium zirconate prepared from the mechanically activated precursor exhibits 4–9 times larger BET surface area relative to that of Gd2Zr2O7 synthesized at the same calcination conditions from the as-prepared precursor. In particular, this is beneficial for preparation of nanostructured dense ceramic materials with enhanced properties. [ABSTRACT FROM AUTHOR]

Structures with Ge/Si nanoparticles (quantum dots) in an aluminum-oxide matrix are of interest due to the combination of two basic semiconductors and the use of a matrix with a high permittivity and strong oxygen–metal bonding. In this study, multilayer nanoperiodic structures in the form of a substrate/Al2O3/Ge/Si/Al2O3...Al2O3 sequence of layers (with the period Al2O3/Ge/Si and the number of periods up to 20) are produced and then annealed at different temperatures. It is shown that, after annealing, the structures contain both Ge and Si crystalline particles, whose dimensions and number are defined by the deposited-layer thicknesses and the annealing temperature. The results obtained by different optical techniques suggest that the structures exhibit the quantum-confinement effect. This inference is supported by high-resolution microscopy. [ABSTRACT FROM AUTHOR]

The processes occurring during the mechanical activation of a-Fe2O3 (hematite) in the presence of oleic acid in a centrifugal-planetary mill have been investigated. Mechanical activation for 10 h afforded hematite powder with particles size of 10–40 nm, as shown by means of X-ray diffraction analysis, FTIR spectroscopy, high-resolution transmission electron microscopy, and specific surface area measurements. Longer milling has led to mechanochemical transformation of hematite into Fe3O4 (magnetite). [ABSTRACT FROM AUTHOR]

The capabilities of metalorganic vapor-phase epitaxy (MOVPE) in fabrication of structures with thin (1–2 nm) alternating InAs/GaSb layers on a GaSb substrate are studied. The characteristics of these structures were examined using transmission electron microscopy and methods of photo- and electroluminescence. It was found that two GaInAsSb solid solutions of different compositions were formed in the active regions of structures in the given growth conditions. The fabricated system was characterized by an emission wavelength of 4.96 μm at a temperature of 77 K. The results reveal new opportunities for bandgap engineering of semiconductor structures based on InAs/GaSb, which are designed for optoelectronic devices operating in the infrared range, provided by MOVPE. [ABSTRACT FROM AUTHOR]

It was shown that the interaction of silver cations in alkaline aqueous solutions with various kinds of silicates, regardless of their chemical and aggregation state, leads to the formation of an exclusively disilicate form of silver salt. We develop procedures for synthesis of nanostructured weakly ordered nonstoichiometric silver disilicate Ag6 –xHxSi2O7 capable of forming aqueous colloids. We study the micellular structure of colloidal particles in these solutions and demonstrate that permeability of silicic acid layers enveloping nanosized salt cores of these micelles depends on pH. Colloidal silver disilicate is found to exhibit a high catalytic activity in photoinduced oxidation of a broad spectrum of different compounds, which is demonstrated for compounds stable in aqueous solutions such as some organic dies and ferrocyanide complex ([Fe(CN ). [ABSTRACT FROM AUTHOR]

The results of experiments on the fabrication (by molecular-beam epitaxy) and investigation of the heterostructures of a two-frequency quantum-cascade laser produced on the basis of a heteropair of In0.53Ga0.47As/Al0.48In0.52As solid solutions on an InP substrate are presented. The heterostructures contained quantum cascades emitting at a wavelength of 9.6 μm and cascades emitting at a wavelength of 7.6 μm. The high structural quality of the fabricated heterostructures is shown. The spontaneous emission and lasing spectra are investigated and the multimodal laser generation of stripe lasers at a wavelength of 7.6 μm is demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: Lasing in MBE-grown impulsively pumped quantum cascade lasers of 9.6 μm at 140 K has been demonstrated. The active area is based on three-phonon resonance scattering of electrons. An In0.53Ga0.47As/Al0.48In0.52As solid alloy heteropair was used to form periods of quantum cascade lasers. The upper In0.52Al0.48As cladding of the waveguide was made thick. Alloyed and unalloyed lower metallization systems were studied. The threshold current density for a ridge laser 1 mm long and 27 μm wide has been found to roughly equal 3 kA/cm2 at 87 K. The optical output power has been estimated at a level of 20-35 mW. [ABSTRACT FROM AUTHOR]

Electron and hole emission from states of a ten-layer system of tunneling-coupled vertically correlated InAs/GaAs quantum dots (QDs) is studied experimentally by capacitance—voltage measurements and deep-level transient spectroscopy. The thickness of GaAs interlayers separating sheets of InAs QDs was ≈3 nm, as determined from transmission electron microscope images. It is found that the periodic multimo-dal DLTS spectrum of this structure exhibits a pronounced linear shift as the reverse-bias voltage Ur applied to the structure is varied. The observed behavior is a manifestation of the Wannier—Stark effect in the InAs/GaAs superlattice, where the presence of an external electric field leads to the suppression of coupling between the wave functions of electron states forming the miniband and to the appearance of a series of discrete levels called Wannier—Stark ladder states. [ABSTRACT FROM AUTHOR]

Epitaxial GaAs layers containing InAs semiconductor quantum dots and As metal quantum dots are grown by molecular beam epitaxy. The InAs quantum dots are formed by the Stranskii-Krastanow mechanism, whereas the As quantum dots are self-assembled in the GaAs layer grown at low temperature with a large As excess. The microstructure of the samples is studied by transmission electron microscopy. It is established that the As metal quantum dots formed in the immediate vicinity of the InAs semiconductor quantum dots are larger in size than the As quantum dots formed far from the InAs quantum dots. This is apparently due to the effect of strain fields of the InAs quantum dots upon the self-assembling of As quantum dots. Another phenomenon apparently associated with local strains around the InAs quantum dots is the formation of V-like defects (stacking faults) during the overgrowth of the InAs quantum dots with the GaAs layer by low-temperature molecular beam epitaxy. Such defects have a profound effect on the self-assembling of As quantum dots. Specifically, on high-temperature annealing needed for the formation of large-sized As quantum dots by Ostwald ripening, the V-like defects bring about the dissolution of the As quantum dots in the vicinity of the defects. In this case, excess arsenic most probably diffuses towards the open surface of the sample via the channels of accelerated diffusion in the planes of stacking faults. [ABSTRACT FROM AUTHOR]