Manfred Ramsteiner

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We report on a method for the fabrication of graphene on a silicon dioxide substrate by solid-state dissolution of an overlying stack of a silicon carbide and a nickel thin film. The carbon dissolves in the nickel by rapid thermal annealing. Upon cooling, the carbon segregates to the nickel surface forming a graphene layer over the entire nickel surface. By(More)
We investigate the magnetic properties of epitaxial GaN:Gd layers as a function of the external magnetic field and temperature. An unprecedented magnetic moment is observed in this diluted magnetic semiconductor. The average value of the moment per Gd atom is found to be as high as 4000 micro(B) as compared to its atomic moment of 8 micro(B). The long-range(More)
Injection of spin polarized electrons from a metal into a semiconductor is demonstrated for a GaAs/(In,Ga)As light emitting diode covered with Fe. The circular polarization degree of the observed electroluminescence reveals a spin injection efficiency of 2%. The underlying injection mechanism is explained in terms of a tunneling process.
We investigate the structural and optical properties of spontaneously formed GaN nanowires with different degrees of coalescence. This quantity is determined by an analysis of the cross-sectional area and perimeter of the nanowires obtained by plan-view scanning electron microscopy. X-ray diffraction experiments are used to measure the inhomogeneous strain(More)
We report resonant Raman scattering (RRS) by the TO, LO, and 2 LO modes of single wurtzite and zincblende GaAs nanowires. The optical band gap of wurtzite GaAs is 1.460 eV± 3meV at room temperature, and 35± 3meV larger than the GaAs zinc-blende band gap. Raman measurements using incoming light polarized parallel and perpendicular to the wire c axis allowed(More)
We report on direct measurements of the impurity band hole polarization in the diluted magnetic semiconductor (Ga,Mn)As. The polarization of impurity band holes in a magnetic field is strongly enhanced by antiferromagnetic exchange interaction with Mn ions. The temperature dependence of the hole polarization shows a strong increase of this polarization(More)
Nanoscale substrates such as nanowires allow heterostructure design to venture well beyond the narrow lattice mismatch range restricting planar heterostructures, owing to misfit strain relaxing at the free surfaces and partitioning throughout the entire nanostructure. In this work, we uncover a novel strain relaxation process in GaAs/InxGa1-xAs core-shell(More)
Efficient infrared light emitters integrated on the mature Si technology platform could lead to on-chip optical interconnects as deemed necessary for future generations of ultrafast processors as well as to nanoanalytical functionality. Toward this goal, we demonstrate the use of GaAs-based nanowires as building blocks for the emission of light with(More)
GaN nanowire ensembles with axial In(x)Ga(1-x)N multi-quantum-wells (MQWs) were grown by molecular beam epitaxy. In a series of samples we varied the In content in the MQWs from almost zero to around 20%. Within the nanowire ensemble, the MQWs fluctuate strongly in composition and size. Statistical information about the composition was obtained from x-ray(More)
We present a systematic, temperature-dependent study of excitonic real-space transfer into single GaAs quantum wires using time-resolved low-temperature near-field luminescence spectroscopy. Excitons generated by local short pulse optical excitation in a 250 nm spot undergo diffusive transport over a length of several micrometres and are subsequently(More)