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Register a new userMBE grown microcavities based on selenium and tellurium compounds
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In this work, we present three groups of microcavities: based on selenium compounds only, based on tellurium compounds only, and structures based on mixed selenium and tellurium compounds. We focus on their possible applications in the field of optoelectronic devices and fundamental physics (VCSELs, narrow range light sources, studies of cavity-polariton electrodynamics) in a range of wavelength from 540 to 760 nm.
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This work presents methods of controlling the density of self-assembled CdTe quantum dots (QDs) grown by molecular beam epitaxy. Two approaches are discussed: increasing the deposition temperature of CdTe and the reduction of CdTe layer thickness. Photoluminescence (PL) measurements at low temperature confirms that both methods can be used for significant reduction of QDs density from 10$^{10}$QD/cm$^2$ to 10$^7$-10$^8$QD/cm$^2$. For very low QDs density, identification of all QDs lines observed in the spectrum is possible.
This paper reports on a detailed magnetotransport investigation of the magnetic anisotropies of (Ga,Mn)As layers produced by various sources worldwide. Using anisotropy fingerprints to identify contributions of the various higher order anisotropy terms, we show that the presence of both a [100] and a [110] uniaxial anisotropy in addition to the primary ([100] + [010]) anisotropy is common to all medium doped (Ga,Mn)As layers typically used in transport measurement, with the amplitude of these uniaxial terms being characteristic of the individual layers.
(Bi1-xSbx)2Se3 thin films have been prepared using molecular beam epitaxy (MBE). We demonstrate the angle-resolved photoemission spectroscopy (ARPES) and transport evidence for the existence of strong and robust topological surface states in this ternary system. Large tunability in transport properties by varying the Sb doping level has also been observed, where insulating phase could be achieved at x=0.5. Our results reveal the potential of this system for the study of tunable topological insulator and metal-insulator transition based device physics.
The recent study of oxides led to the discovery of several new fascinating physical phenomena. High-temperature superconductivity, colossal magnetoresistance, dilute magnetic doping, or multiferroicity were discovered and investigated in transition-metal oxides, representing a prototype class of strongly correlated electronic systems. This development was accompanied by an enormous progress regarding thin film fabrication. Within the past two decades, epitaxial thin films with crystalline quality approaching semiconductor standards became available using laser molecular beam epitaxy. This evolution is reviewed, particularly with emphasis on transition-metal oxide thin films, their versatile physical properties, and their impact on the field of spintronics. First, the physics of ferromagnetic half-metallic oxides, such as the doped manganites, the double perovskites and magnetite is presented together with possible applications based on magnetic tunnel junctions. Second, the wide bandgap semiconductor zinc oxide is discussed particularly with regard to the controversy of dilute magnetic doping with transition-metal ions and the possibility of realizing p-type conductivity. Third, the field of oxide multiferroics is presented with the recent developments in single-phase multiferroic thin film perovskites as well as in composite multiferroic hybrids.
We demonstrate first measurements of successful spin generation in crystalline Co$_2$FeSi/MgO/GaAs hybrid structures grown by molecular-beam epitaxy (MBE), with different MgO interlayer thicknesses. Using non-local spin valve and non-local Hanle measurement configurations, we determine spin lifetimes of ${tau approx 100}$~ns and spin diffusion lengths of ${lambda approx 5.6}$~$mu$m for different MgO layer thicknesses proving the high quality of the GaAs transport channel. For an optimized MgO layer thickness, the bias dependence of the spin valve signals indicates the verification of the half-metallic gap (upper edge) of Co$_2$FeSi in accordance with first principle calculations. In addition to that, spin generation efficiencies up to 18$%$ reveal the high potential of MgO interlayers at the Co$_2$FeSi/GaAs interface for further device applications.
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