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We report the results of systematic Raman spectroscopy studies of AlxGa1 –xN (x ~ 0.75) layers grown using plasma-assisted molecular beam epitaxy at various stoichiometric conditions and growth fluxes. The high-intensity asymmetric low-frequency peak obeying Bose statistics is discovered in Raman spectra of the layers grown by temperature-modulated epitaxy at strongly Ga-enriched conditions. Theoretical model is developed to explain the origin and the high intensity of the observed low-frequency peak, which is attributed to the presence of excessive metallic gallium in AlGaN layers and can be explained by vibrations of gallium clusters with a diameter of ~1 nm. The nature of the low-frequency peak is similar to that of the boson peak in glasses, which occupies the same frequency range in Raman spectra. We demonstrate the capabilities of Raman spectroscopy as an express and non-destructive technique for optimization of growth conditions of AlGaN layers to achieve simultaneously the atomically-smooth droplet-free surface morphology and the high structural quality. [ABSTRACT FROM AUTHOR]

In situ stress generation and relaxation in AlGaN/GaN/AlN heterostructure with an overall thickness exceeding 3 μm in the process of its growth on a 6 H-SiC substrate by low-temperature plasma-assisted molecular-beam epitaxy at substrate temperatures ranging from 690 to 740°C was studied. At room temperature, AlN and GaN layers revealed residual compressive stresses of-2.3 and-0.1 GPa, respectively. This made it possible to avoid cracking during postgrowth cooling of the structure. [ABSTRACT FROM AUTHOR]

We report on comparative studies of the emission properties of CdSe/ZnSe quantum dots (QDs) grown by molecular beam epitaxy either with or without predeposition of a sub-monolayer CdTe stressor, and in the latter case, either with or without in-situ thermal annealing. The emission of a limited number of QDs was registered in all samples by micro-photoluminescence confocal spectroscopy through 500-nm-size round apertures opened in a non-transparent gold mask by ball assisted etching technique. The measurements reveal the lowest density of emitting QDs in the sample grown with the in-situ annealing that is attributed to both ripening of the CdSe QDs and strain relaxation in the largest QDs, followed by formation of defects serving as centres of nonradiative recombination. The employment of the CdTe stressor causes narrowing of the total QDs emission band and simultaneous broadening of the single-QD lines that is consistent with the formation of a relatively homogeneous dense array of type-I CdSe/ZnSe QDs adjoining type-II Zn(Cd)Te/ZnSe nanostructures. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We report on fabrication and studies of composite heterostuctures consisting of an Al0.55Ga0.45N/Al0.8Ga0.2N quantum well and surface Al nanoislands, grown by plasma-assisted molecularbeam epitaxy on c-sapphire substrates. The influence of a substrate temperature varied between 320 and 700ºC on the size and density of the deposited Al nanoislands is evaluated. The effect of Al nanoislands on decay kinetics of the quantum well middle-ultraviolet photoluminescence has been investigated by time resolved photoluminescence. The samples with the maximum density of Al nanoislands of 108 cm-2 and lateral dimensions in the range of 100-500 nm demonstrated shortening of the photoluminescence lifetime, induced by interaction of the emitting quantum well and the plasmonic metal particles. [ABSTRACT FROM AUTHOR]

Advances in the production technology of multiperiod nanoheterostructures of quantum-cascade lasers with 60 cascades by molecular-beam epitaxy (MBE) on an industrial multiple-substrate MBE machine are discussed. The results obtained in studying the nanoheterostructures of quantum-cascade lasers by transmission electron microscopy, high-resolution X-ray diffraction analysis, and photoluminescence mapping are presented. [ABSTRACT FROM AUTHOR]

Arrays of (Ga, Mn)As nanowire crystals are synthesized by molecular-beam epitaxy. Electronbeam lithography made possible the fabrication of electric contacts to individual nanowires. The influence of the annealing temperature on the properties of the contacts is studied. The optical annealing temperature is determined to be 160°C. It is found that an increase in the annealing temperature yields structure degradation. From studies of the current-voltage characteristics of the individual nanowire structures, a number of their electrical parameters, such as the resistivity and the mobility of charge carriers are determined. [ABSTRACT FROM AUTHOR]

Features of the growth of InAs quantum dots in an AlGaAs matrix by molecular beam epitaxy at different substrate temperatures, deposition rates, and amounts of deposited InAs are studied. The optimum conditions for growing an array of low-density (≤2 × 10 cm) small (height of no more than 4 nm) self-organized quantum dots are determined. The possibility of the formation of optically active InAs quantum dots emitting in the energy range 1.3-1.4 eV at a distance of no more than 10 nm from the coherent heterovalent GaAs/ZnSe interface is demonstrated. It is established that inserting an optically inactive 5-nm GaAs quantum well resonantly coupled with InAs quantum dots into the upper AlGaAs barrier layer enhances the photoluminescence efficiency of the quantum-dot array in hybrid heterostructures. [ABSTRACT FROM AUTHOR]

We show that InAs quantum dots (QDs) can be grown by molecular beam epitaxy (MBE) with an ultralow density of sin 10 cm without any preliminary or post-growth surface treatment. The strain-induced QD formation proceeds via the standard Stranski-Krastanow mechanism, where the InAs coverage is decreased to 1.3-1.5 monolayers (MLs). By using off-cut GaAs (100) substrates, we facilitate the island nucleation in this subcritical coverage range without any growth interruption. The QD density dependences on the InAs coverage are studied by photoluminescence, atomic force microscopy, transmission electron microscopy, and are well reproduced by the universal double exponential shapes. This method enables the fabrication of InAs QDs with controllable density in the range 10-10 cm, exhibiting bright photoluminescence. [ABSTRACT FROM AUTHOR]

Self-assembled quantum dots (SQDs) based on (In,Mn)As solid solutions have been synthesized by molecular beam epitaxy on GaAs(100) substrates. Examination of the surface morphology of samples by the method of atomic force microscopy showed that the presence of Mn influences the surface density and dimensions of SQDs. The effect of a preliminarily deposited sublayer of Mn atoms on the properties of subsequently grown layers with (In,Mn)As quantum dots has been studied. [ABSTRACT FROM AUTHOR]