Screening of the quantum-confined Stark effect in AlN/GaN nanowire superlattices by Germanium doping

We report on electrostatic screening of polarization-induced internal electric fields in AlN/GaN nanowire heterostructures with Germanium-doped GaN nanodiscs embedded between AlN barriers. The incorporation of Germanium at concentrations above $10^{20}\,\text{cm}^{-3}$ shifts the photoluminescence emission energy of GaN nanodiscs to higher energies accompanied by a decrease of the photoluminescence decay time. At the same time, the thickness-dependent shift in emission energy is significantly reduced. In spite of the high donor concentration a degradation of the photoluminescence properties is not observed.Comment: Manuscript including Supplemental material (15 pages, 5 figures

Universality of electron accumulation at wurtzite c- and a-plane and zinc-blende InN surfaces

Electron accumulation is found to occur at the surface of wurtzite (112¯0), (0001), and (0001¯) and zinc-blende (001) InN using x-ray photoemission spectroscopy. The accumulation is shown to be a universal feature of InN surfaces. This is due to the low Г-point conduction band minimum lying significantly below the charge neutrality level

Long-lived excitons in GaN/AlN nanowire heterostructures

GaN/AlN nanowire heterostructures can display photoluminescence (PL) decay times on the order of microseconds that persist up to room temperature. Doping the GaN nanodisk insertions with Ge can reduce these PL decay times by two orders of magnitude. These phenomena are explained by the three-dimensional electric field distribution within the GaN nanodisks, which has an axial component in the range of a few MV/cm associated to the spontaneous and piezoelectric polarization, and a radial piezoelectric contribution associated to the shear components of the lattice strain. At low dopant concentrations, a large electron-hole separation in both the axial and radial directions is present. The relatively weak radial electric fields, which are about one order of magnitude smaller than the axial fields, are rapidly screened by doping. This bidirectional screening leads to a radial and axial centralization of the hole underneath the electron, and consequently, to large decreases in PL decay times, in addition to luminescence blue shifts

Aerosol filter characterization by electron microscopical methods

Ein neues Verfahren zur Prüfung und Charakterisierung von Aerosolfiltern wird beschrieben. Die Wirkungsgrade werden mit Hilfe eines Transmissions-Elektronenmikroskop gemessen. Das Verfahren ist sehr empfindlich und hat sich in der Praxis gut bewährt. (IUCT

Filtration and diffusion of asbestos fibers

Mit Hilfe eines feindispensen faserigen Aerosols wurden die Abscheidung von Fasern in analytischen Filtern und die Diffusionsbewegung gemessen. Die gemessenen Diffusions-Koeffizienten lagen zwischen 0,6-2,0.10 hoch -5 qcm/s und waren höher als die von der Theorie zu erwarteten Ergebisse. Auch die Abscheidgrade in den Filtern waren höher als bei den sphärischen Partikeln

Antimony in the environment - first results from the German environmental specimen bank: Poster at the 1st International Workshop on Antimony in the Environment, 16.05.-19.05.2005, Heidelberg

Research Program The German Environmental Specimen Bank (ESB) is an important tool for the long-term monitoring of pollutants in typical ecosystems. Within this program for example in terrestrial ecosystems spruce needles (Picea abies), beech leaves (Fagus sylvatica) and Lombardy poplar (Populus nigra 'Italica') are sampled at different locations in Germany. The specimens are archived and analyzed for environmental relevant substances. The spruce is widespread in Central Europe. Its suitability as a specimen type for the ESB is founded on its economic and ecological significance and the considerable understanding of its pattern of accumulation in relation to many hazardous substances. The target organ is the one-year-old shoot which, when sampled in spring (February to late May before sprouting begins), presents a comprehensive picture of winter pollution in the environment. The common, or European, beech plays a dominant role in most nearly natural and also anthropogenically influenced forest ecosystems in Central Europe. Unlike the coniferous spruce, it prefers lower altitudes. The leaves are the target organ. Sampling takes place in the late summer before the leaves begin to change colour (August to mid-September). The sampling of biota within the ESB program is performed by University of Trier. Results On the poster we present first results on antimony levels. The antimony was co-analyzed with arsenic using hydride-generation ICP-MS with cool plasma/ShieldTorch. For optimum sensitivity, accuracy and precision Sb (As) must be pre-reduced to the most efficient oxidation state for hydride formation. A solution of KI plus ascorbic acid is used. Before analyses the material is digested with a high pressure microwave system (MLS ULTRAClave II). Spruce shoots and leaves showed Sb levels in the ng/g range (dry matter)

Intraband Absorption in Self-Assembled Ge-Doped GaN/AlN Nanowire Heterostructures

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