Investigation of a contacting scheme for self-assembled cleaved edge overgrown InAs nanowires and quantum dot arrays

A contacting scheme to measure the transport properties into self-assembled InAs Quantum Wires (QWRs) or Quantum Dots (QDs) is presented. The nanostructures are formed on the (110) cleaved edge of a AlAs/AlGaAs heterostructure substrate by means of the Cleaved Edge Overgrowth (CEO) technique and Molecular Beam Epitaxy (MBE). The InAs nanostructure grows directly on top of the AlAs layer, which hosts a two dimensional electron gas (2DEG). In a transistor-like schematic of the device, the 2DEG acts as a contact to the InAs nanostructure. A top gate is used to deplete the 2DEG, thereby defining the InAs nanostructure as a channel L between source and drain. Measurements confirm that the device can be operated as a field-effect transistor, but no evidence of a current flow through the InAs QWRs can be found. Numerical calculations of the electron density and the device band structure confirm that a depletion zone is present in the AlAs layer close to the cleaved edge and the InAs QWR seems electrically isolated from the AlAs 2DEG leads. Possible solutions could be an additional Schottky gate contact on the CEO side or selective doping inside the CEO barrier. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised protons

Measurements of the Collins and Sivers asymmetries for charged pions and charged and neutral kaons produced in semi-inclusive deep-inelastic scattering of high energy muons off transversely polarised protons are presented. The results were obtained using all the available COMPASS proton data, which were taken in the years 2007 and 2010. The Collins asymmetries exhibit in the valence region a non-zero signal for pions and there are hints of non-zero signal also for kaons. The Sivers asymmetries are found to be positive for positive pions and kaons and compatible with zero otherwise. © 2015

Measurement of azimuthal hadron asymmetries in semi-inclusive deep inelastic scattering off unpolarised nucleons

Spin-averaged asymmetries in the azimuthal distributions of positive and negative hadrons produced in deep inelastic scattering were measured using the CERN SPS longitudinally polarised muon beam at 160GeV/c and a 6LiD target. The amplitudes of the three azimuthal modulations cos φh, cos 2φh and sin φh were obtained binning the data separately in each of the relevant kinematic variables x, z or pTh and binning in a three-dimensional grid of these three variables. The amplitudes of the cos φh and cos 2φh modulations show strong kinematic dependencies both for positive and negative hadrons. © 2014 CERN for the benefit of the COMPASS Collaboration

Growth optimization and characterization of high mobility two-dimensional electron systems in AlAs quantum wells

2D Elektronsysteme in Aluminium Arsenide (AlAs) wurden im Rahmen dieser Doktorarbeit gewachsen, optimiert und charakterisiert. Hochbewegliche (001)- und (110)- orientierte AlAs Quantum Wells (QWs), bzw. (001)-orientierte AlAs QW Proben in der „Thin cap“ Geometrie, wurden gewachsen. Es wurde experimentell nachgewiesen, dass (001)-orientierte AlAs dicke QWs „double-valley“ und (110)-orientierte AlAs dicke QWs „single-valley“ Besetzung haben. Die beste Proben zeigen eine unerwartete zunehmende Beweglichkeit mit sinkender Temperatur zwischen 4 K und 300 mK. Die Form dieser Temperaturabhängigkeit ist unkonventionell im Vergleich mit GaAs. Beweglichkeitsanisotropie für (110)-orientierte AlAs QWs wurde beobachtet.2D Elektronsysteme in Aluminium Arsenide (AlAs) wurden im Rahmen dieser Doktorarbeit gewachsen, optimiert und charakterisiert. Hochbewegliche (001)- und (110)- orientierte AlAs Quantum Wells (QWs), bzw. (001)-orientierte AlAs QW Proben in der „Thin cap“ Geometrie, wurden gewachsen. Es wurde experimentell nachgewiesen, dass (001)-orientierte AlAs dicke QWs „double-valley“ und (110)-orientierte AlAs dicke QWs „single-valley“ Besetzung haben. Die beste Proben zeigen eine unerwartete zunehmende Beweglichkeit mit sinkender Temperatur zwischen 4 K und 300 mK. Die Form dieser Temperaturabhängigkeit ist unkonventionell im Vergleich mit GaAs. Beweglichkeitsanisotropie für (110)-orientierte AlAs QWs wurde beobachtet