This work reports a novel low-temperature approach for the direct heteroepitaxial integration of narrow-bandgap III-V materials on silicon. We demonstrate the self-catalyzed vapor-liquid-solid molecular beam epitaxy growth of InAs : Bi nanowires via Bi catalytic droplets directly on Si (111) substrates. Compared to Au-catalyzed growth, bismuth-induced vapor-liquid-solid synthesis improves the compatibility of the proposed low-thermal-budget fabrication technique with the silicon platform. The nanowire geometry enables the direct synthesis of dislocation-free zinc blende InAs : Bi nanowires on silicon with a Bi content of 0.05%. The bismuth concentration in NWs growing from Bi droplets is consistent with the Bi solubility limit in bulk InAs, suggesting that equilibrium thermodynamics plays a dominant role in Bi incorporation during VLS growth. Additionally, Bi incorporation facilitates a material bandgap reduction, which is confirmed theoretically and experimentally. Thus, the proposed approach enables a promising route for the monolithic integration of high-performance mid-infrared devices in silicon photonics.

Epitaxial bismuth planar nanostructures and nanowires grown on CaF 2 /Si(111) exhibit broadband photoluminescence.

Objective: The aim of this work is to study bulk GaPN and GaPNAs layers grown by molecular beam epitaxy on silicon substrates. The optical properties of the heterostructures were investigated using photoluminescence. The technique of time-resolved photoluminescence (or photoluminescence kinetics) was employed to evaluate the carrier lifetime in bulk GaPN and GaPNAs layers. Experimental: An investigation of the influence of the buffer layer on the heterostructure characteristics was conducted. The photoluminescence intensity in the bulk GaPN layer was found to be virtually identical for heterostructures employing either a buffer layer grown by Migration-Enhanced Epitaxy (MEE-GaP buffer) or a GaP buffer layer grown with a gradual temperature ramp from 450 to 600 °C. Conclusion: It was shown that the lifetime of minority carriers in the bulk GaPN layer grown on a silicon substrate is determined to a greater extent by defects introduced during the nitrogen incorporation into the GaP lattice, rather than by defects caused by growth on silicon substrate

The paper examines the basic physical principles of the operation of terahertz (THz) polarization converters and discusses the main types of polarizers, including those based on wire girds, films, metamaterials, etc. More sophisticated devices based on polarizers made of stacks of segmented, achromatic, and tunable composite waveplates, including those operating over a wide wavelength range, and on THz polarization filters are considered. The basic principles of their calculation using the Jones formalism are described.

In this study, we present the selective area plasma-assisted molecular beam epitaxial growth of GaP-based nanoheterostructures (nanostubs), incorporating direct bandgap GaAsP or GaPN segments, on patterned SiO2/Si(001) wafers. A microsphere optical lithography and anisotropic Si wet-etching techniques were employed for wafer-scale surface patterning through SiO2 growth mask, allowing to obtain either planar or pyramidal pit nucleation site morphologies. X-ray diffraction reciprocal space mapping and Raman microspectroscopy studies confirm compositional homogeneity of the nanostub arrays. The dilute nitride nanostubs display the narrowest and most intense visible red photoluminescence response at room temperature, which is an order of magnitude higher compared to the GaAsP ones. The formation of the nitrogen sub-band in GaPN alloy was confirmed in the framework of density functional theory, providing insights for interpreting the experimental results. These findings demonstrate the feasibility of the proposed approach for fabricating the ordered arrays of nanoscale visible light emitters on silicon.

We study the growth of nanowire arrays based on InAsP on silicon substrates. It was found that during the growth process two structural phases are formed: a cubic structure of the sphalerite type and a hexagonal structure of the wurtzite type. The epitaxial relations between InAsP and Si were determined: [0001]NWs || [111]Si, [ 112̅0 ]NWs || [ 11̅0 ]Si. A decrease of the radial growth rate and the formation of an axial heterojunction were revealed with the formation of thin (<100 nm) segments of the InAs1 – xPx solid solution and maintaining a sufficiently high partial pressure of the As flow (at least 50

Photoluminescence of arrays of self-induced nanowires consisting of pure InAs and of InAs diluted with nitrogen was studied in the 4.2-300 K temperature range. Formation of the hexagonal wurtzite (nanowires) and cubic sphalerite (mostly parasitic islands) crystal structure modifications was observed on a Si substrate used for the growth of the nanowires. A decrease in the band gap of both crystalline phases due to the introduction of nitrogen was established.

Epitaxial InAs-based nanowire (NW) arrays have recently gained attention as promising materials for infrared optoelectronics. To shift the spectral sensitivity of NW-based photodetectors, we for the first time investigated dilute nitride InAsN nanowires on Si(111). The growth of InAsN nanowires with a wurtzite phase was achieved through a self-induced mechanism using plasma-assisted molecular beam epitaxy. Two growth strategies were employed to synthesize InAsN and InAs/InAsN core-shell nanowires, allowing for independent control over the morphology and optical properties. According to the photoluminescence measurement and performed ab initio calculations for the wurtzite InAsN structure, we estimate the atomic concentration of the incorporated nitrogen in the studied structure as 0.5-0.7%. Transmission electron microscopy and X-ray diffraction reveal a wurtzite crystal lattice volume shrinkage with an increase in nitrogen content. Our results demonstrate the potential of dilute nitride InAsN for strain and band gap engineering in NW photodetectors on Si.

n the paper, the influence of growth factors and silicon surface condition on the epitaxial formation of single-domain GaP buffer layers on Si (001) has been studied. A novel two-stage growth technique for the epitaxial building-up of this structure has been put forward and developed. In contrast to using the migration enhanced epitaxy technique, the proposed technology allows one to separate the nucleation and growth stages, to control the doping profile of the GaP buffer layers. The latter is important for further functional applications. The main factors determining the orientation of GaP crystalline lattice when it nucleates on the Si vicinal surface were found. The structural perfection of the grown buffer layers at both stages was proved through careful control by TEM, RHEED, AFM, and HRXRD. These findings have important implications for further functional applications

Epitaxial arrays of the InAs1-xNx core-shell nanowires have been synthesized on Si (111) for the first time. The growth of the nanowires with a wurtzite- type crystal structure was demonstrated by a self- induced mechanism using the molecular beam epitaxy with plasma-assisted nitrogen activation. Using the transmission electron microscopy and X-ray diffraction analysis, a volume decrease in the wurtzite crystal unit cell with increasing nitrogen content was revealed.

Crystal phase and strain engineering in epitaxial nanowire (NW) heterostructures provide a widely tunable functionality for future nanoscale light emitters and photodetectors. Thus, InAs band gaps can be finely tuned in the mid -infrared range by introducing a mechanical strain through lattice mismatch in core-shell NWs. Here, we demonstrate that the inhomogeneity of the InP shell thickness leads to a non-uniform stress field and a local variation in the degree of surface passivation along the InAs NW length which both have a strong effect on the recombination mechanisms. Catalyst-free InAs NWs with a coherent nanometer thick InP shell were grown on Si(111) by means of molecular beam epitaxy. Temperature-dependent photoluminescence (PL) studies (5-150 K) allow us to distinguish the surface passivation and strain-induced effects. Non-trivial temperature dependence in contrast to the expected monotonic band gap shrinkage with temperature was found. At high temperatures (100-150 K), radiative recombination predominantly occurs in the NW regions, which have a thicker InP shell and, as a result, are free from surface states. In turn, the coherently grown InP shell induces a tensile strain in the InAs NW core and leads to a blue shift in an emission energy by a 45-50 meV at 100 K. In contrast, at low temperatures (<100 K), the PL band undergoes a red shift with decreasing temperature since photogenerated carriers are able to radiatively recombine at band gap energy minima at the unstrained NW regions. According to the performed ab initio calculations, observed emission is attributed to the interband optical transitions of the hexagonal InAs polytype with an intermediate band gap energy (435 meV at 5 K) lying between the zinc-blende and wurtzite values. Current observations are in a great demand for stress -induced band in the functional nanoheterostructures.

We have optimized the growth parameters of the buffer layer for further Pb1-xSnxTe (x >= 0.4) deposition from the point of view of smoothness and crystalline quality. The latter has the properties of a crystalline topological insulator. A three-component hetero-structure consisting of fluorite CaF2, BaF2, and cubic Pb0.7Sn0.3Te:In layers was formed on the Si(111). The surface morphology of this hybrid heterostructure was studied depending on the growth temperature and the thickness.

Hybrid ferromagnet-semiconductor systems possess new outstanding properties, which emerge when bringing magnetic and semiconductor materials into contact. In such structures, the long-range magnetic proximity effect couples the spin systems of the ferromagnet and semiconductor on distances exceeding the carrier wave function overlap. The effect is due to the effective p-d exchange interaction of acceptor-bound holes in the quantum well with d-electrons of the ferromagnet. This indirect interaction is established via the phononic Stark effect mediated by the chiral phonons. Here, we demonstrate that the long-range magnetic proximity effect is universal and observed in hybrid structures with diverse magnetic components and potential barriers of various thicknesses and compositions. We study hybrid structures consisting of a semimetal (magnetite Fe3O4) or dielectric (spinel NiFe2O4) ferromagnet and a CdTe quantum well separated by a nonmagnetic (Cd,Mg)Te barrier. The proximity effect is manifested in the circular polarization of the photoluminescence corresponding to the recombination of photoexcited electrons with holes bound to shallow acceptors in the quantum well induced by magnetite or spinel itself, in contrast to interface ferromagnet in case of metal-based hybrid systems. A nontrivial dynamics of the proximity effect is observed in the studied structures due to recombination-induced dynamic polarization of electrons in the quantum well. It enables the determination of the exchange constant Δexch ≈ 70 μeV in a magnetite-based structure. The universal origin of the long-range exchange interaction along with the possibility of its electrical control offers prospects for the development of low-voltage spintronic devices compatible with existing solid-state electronics.

We have optimized the growth conditions of the buffer layer for further deposition of Pb1-xSnxTe (x≥0.4), which has the properties of a crystalline topological insulator. To this end, a three-component heterostructure consisting of CaF2, BaF2, and Pb0.7Sn0.3Te : In layers was formed and optimized on the Si(111) surface. The surface morphology of this structure was studied depending on the temperature growth regimes and the optimal combination of growth parameters was selected from the point of view of smoothness and crystalline quality. Keywords: crystalline topological insulator, molecular beam epitaxy, reflection high-energy electron doffraction, atomic force microscopy, Pb0.7Sn0.3Te : In.

Magnetization reversal in as-grown and annealed NiFe2O4 / SrTiO3(0 0 1) epitaxial heterostructures, prepared by laser molecular beam epitaxy (LMBE), was studied using magneto-optical technique in geometry of polar (PMOKE) and longitidual (LMOKE) Kerr effect. It was found that the hysteresis loops of polarization plane rotation and ellipticity measured in LMOKE geometry are combinations of symmetric (even in magnetic field) SPart and antisymmetric (odd in magnetic field) AsPart parts, caused by quadratic (QMOKE ∼ MiMj) and linear (LMOKE ∼ Mi) in magnetization M contributions, correspondingly. The angular dependences of SPart demonstrate in-plane biaxial magnetic anisotropy (BMA) and show that magnetization reversal in as-grown structures occurs by one jump (1j) process, in contrast to the annealed structures, in which two jumps (2j) process takes place when the deviation of magnetic field from the hard axis is less than ∼20°. Analysis within the framework of the Stoner-Wohlfarth (SW) model with account of domain mechanism of magnetization jumps shows that the first jump occurs due to formation and movement of domain walls. Second jump is remarkably diffused, that is associated with the dispersion of the biaxial anisotropy field Ha and misorientations of the magnetic easy axes in different regions of the film. Narrow and strong FMR lines are observed in the most perfect structures in which the diffusion of the second jump is small. The degree of second jump diffusion can be used to assess the structural perfection of the films.

We have optimized the growth conditions of the bufferlayer for further deposition of Pb1−x SnxTe (x ≥ 0.4), which hasthe properties of a crystalline topological insulator. To this end,a three-component heterostructure consisting of CaF2, BaF2, andPb0.7Sn0.3Te : In layers was formed and optimized on the Si(111)surface. The surface morphology of this structure was studieddepending on the temperature growth regimes and the optimalcombination of growth parameters was selected from the point ofview of smoothness and crystalline quality.

Selection and optimization of the technological parameters of growth of Pb0.7Sn0.3Te layers with a thickness up to 300 nm grown on a Si(111) surface at a temperature of 230 to 400°C is carried out. The surface morphology of the resulting films is studied, and the epitaxial relations are determined. It is shown that, depending on the growth temperature, the surface morphology ranges from smooth micrometer-sized islands with monoatomic steps on their surface to narrower terraces.

Magnetization reversal in as-grown and annealed NiFe2O4 / SrTiO3(001) epitaxial heterostructures, prepared by laser molecular beam epitaxy (LMBE), was studied using magneto-optical technique in geometry of polar (PMOKE) and longitidual (LMOKE) Kerr effect. It was found that the hysteresis loops of polarization plane rotation and ellipticity measured in LMOKE geometry are combinations of symmetric (even in magnetic field) SPart and antisymmetric (odd in magnetic field) AsPart parts, caused by quadratic (QMOKE similar to MiMj) and linear (LMOKE similar to M-i) in magnetization M contributions, correspondingly. The angular dependences of SPart demonstrate in-plane biaxial magnetic anisotropy (BMA) and show that magnetization reversal in as-grown structures occurs by one jump (1(j)) process, in contrast to the annealed structures, in which two jumps (2(j)) process takes place when the deviation of magnetic field from the hard axis is less than similar to 20 degrees. Analysis within the framework of the Stoner-Wohlfarth (SW) model with account of domain mechanism of magnetization jumps shows that the first jump occurs due to formation and movement of domain walls. Second jump is remarkably diffused, that is associated with the dispersion of the biaxial anisotropy field H-a and misorientations of the magnetic easy axes in different regions of the film. Narrow and strong FMR lines are observed in the most perfect structures in which the diffusion of the second jump is small. The degree of second jump diffusion can be used to assess the structural perfection of the films.

The possibility of epitaxial growth of Pb0.7Sn0.3Te crystalline topological insulator films on the Si(111) surface was shown and epitaxial relations were found. It was shown that, depending on the growth temperature, it is possible to control not only the character of the morphology, but also, to a significant extent, the smoothness of the epitaxial layer surface, which is extremely important for further transport measurements of the films. Analysis of the grown films surface morphology made it possible to establish the average value of the height and lateral size of the terraces and islands forming Pb0.7Sn0.3Te surface.