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Strain-induced changes of ZnTe energy gap in ZnTe/ZnMgTe core/shell nanowires arising from lattice mismatch between the core and the shell semiconductor are studied by means of optical methods. It is shown that the increase of the Mg content in the shell, as well as the increase of the shell thickness result in an effective redshift of the near band edge photoluminescence from ZnTe nanowire cores, which reflects directly the decrease of energy gap under tensile strain conditions. The conclusions are supported by theoretical calculations in terms of the valence force field model. The observed change of ZnTe energy gap can be as large as 120 meV with respect to the unstrained conditions and can be tuned in a continuous manner by adjusting shell parameters, which open a path towards an effective band gap engineering in these structures. [ABSTRACT FROM AUTHOR]

We report on an approach to fabricate ZnTe-based core/shell radial heterostructures containing ZnO, as well as on some of their physical properties. The molecular beam epitaxy grown ZnTe nanowires constituted the core of the investigated structures and the ZnO shells were obtained by thermal oxidation of ZnTe NWs. The influence of the parameters characterizing the oxidation process on selected properties of core/shell NWs were examined. Scanning electron microscopy revealed changes of the NWs morphology for various conditions of the oxidation process. X-ray diffraction, high resolution transmission electron microscopy, and Raman scattering measurements were applied to reveal the presence of ZnTe single crystal core and polycrystalline ZnO-shell of investigated structure. [ABSTRACT FROM AUTHOR]

Systematic studies of neutral heavy-hole excitonic line energy changes in a strong excitation regime were carried out by means of a pump-probe method for quantum wells containing a 2D gas of free holes. Energy shift of Xe1hh1 line was analyzed for different excitation energies at fixed delay between pump and probe pulses, also under external magnetic field. It was observed that this shift depends not only on the density of created excitons but also directly on the pump energy. In co-polarization configuration for excitation energy below an absorption resonance the energetic blue shift rises linearly with the elevated exciton density (localized excitons are created). For energies slightly above the resonance, the blue shift diminishes dramatically in spite of high exciton density present (delocalized excitons are created). Model absorption calculations are in qualitative agreement with the experimental data. [ABSTRACT FROM AUTHOR]

From a Raman scattering investigation of folded longitudinal acoustic phonons in zinc-blende CdTe/MgTe superlattices, we demonstrate that this pair of materials displays a large acoustic impedance mismatch Z1/Z2=1.39, which opens promising perspectives for acoustic phonon engineering in semiconductor nanodevices. The determined MgTe sound velocity s=(3.35±0.15)×103 m/s agrees well with ab initio predictions for the same crystalline form. [ABSTRACT FROM AUTHOR]

We demonstrate a method to electrically manipulate the spin polarization in a semiconductor on a micrometer length scale and a submicrosecond time scale. A variable magnetic field induced by a microscale current loop magnetizes the Mn2+ ions in a CdMnTe/CdMgTe diluted magnetic semiconductor quantum well, and via sp-d exchange interaction polarizes photogenerated electron-hole pairs. A maximum spin polarization degree of ±8.5% is obtained at 4.2 K without external magnetic field. The induced carrier spin polarization and the thermal heating of Mn2+ spins are resolved spatially and temporally by microphotoluminescence measurements. [ABSTRACT FROM AUTHOR]

We report on the study of two-step grown crystalline II-VI semiconductor nanowires (NWs) covered with ferromagnetic metal. In the first step ZnTe nanowires were grown by a vapor-liquid-solid mechanism (VLS) on GaAs (1 1 1)B substrates covered with Au thin film. Solid source molecular beam epitaxy and Au-based nanocatalysts were used for these purposes. The nanowires were smooth, slightly tapered and mostly oriented along the axis perpendicular to the substrate. The diameters of the obtained nanowires were from 30 to 70 nm and their length was around 1 µm. In the second step the nanowires were covered with Co shell of different thicknesses. As a result magnetic nanotubes were formed. Structural characterization of the nanowires was performed using scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy techniques. Initial roughness of the nanowires influences the growth of Co shell with the increment of deposition thickness. Deposited Co formed nanograins having hexagonal closed packed structure, however face cubic centered grains were also observed. Magnetic force microscopy experiments on an individual Co nanotube revealed magnetic anisotropy of the investigated structures. [ABSTRACT FROM AUTHOR]

The exchange interaction between magnetic ions and charge carriers in semiconductors is considered to be a prime tool for spin control. Here, we solve a long-standing problem by uniquely determining the magnitude of the long-range p - d exchange interaction in a ferromagnet-semiconductor (FM-SC) hybrid structure where a 10-nm-thick CdTe quantum well is separated from the FM Co layer by a CdMgTe barrier with a thickness on the order of 10 nm. The exchange interaction is manifested by the spin splitting of acceptor bound holes in the effective magnetic field induced by the FM. The exchange splitting is directly evaluated using spin-flip Raman scattering by analyzing the dependence of the Stokes shift ΔS on the external magnetic field B. We show that in a strong magnetic field, ΔS is a linear function of B with an offset of Δpd = 50-100 μeV at zero field from the FM induced effective exchange field. On the other hand, the s - d exchange interaction between conduction band electrons and FM, as well as the p - d contribution for free valence band holes, are negligible. The results are well described by the model of indirect exchange interaction between acceptor bound holes in the CdTe quantum well and the FM layer mediated by elliptically polarized phonons in the hybrid structure. [ABSTRACT FROM AUTHOR]