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@MASTERSTHESIS{Guesken:820938,
      author       = {Guesken, Nicholas},
      othercontributors = {Lepsa, Mihail Ion},
      title        = {{MBE} growth and characterization of {T}e-doped {I}n{A}s
                      nanowires and {I}n{A}s/superconductor hybrid structures},
      school       = {RWTH Aachen University},
      type         = {MS},
      reportid     = {FZJ-2016-06202},
      pages        = {122p.},
      year         = {2016},
      note         = {RWTH Aachen University, Masterarbeit, 2016},
      abstract     = {This work investigates the growth mechanism of tellurium
                      doped InAs/superconductor hybrid structures as well as their
                      electrical properties. Semiconductor/superconductor
                      structures are of interest for both, fundamental research
                      and applied science. The junctions might become an important
                      building block in future quantum computing networks.
                      However, already in present time gate-controllable Josephson
                      junctions constitute an attractive system for research and
                      applications.One part of this thesis is devoted to the
                      doping mechanism of InAs nanowires using the group VI
                      material tellurium. Nanowire doping is of great interest for
                      a broad range of applications such as field-effect
                      transistors, p-n junctions and optoelectronic devices. In
                      case of gateable Josephson junctions, they constitute an
                      important component, as successfully doped wires lead to a
                      higher critical current Ic, i.e. an enhanced superconducting
                      gap. Applying simple two-point but also field effect
                      measurements, we find that Te-doping is indeed effective.
                      The impact of the tellurium incorporation onto the
                      morphology as well as the crystal structure is investigated
                      using SEM, TEM and XRD measurements. The TEM and XRD
                      measurements are enabled by co-operations with other groups.
                      The results show that the occurrence of zinc blende segments
                      within the wurtzite dominated crystal structure is enhanced
                      due to Te-doping. Moreover, the addition of Te adatoms
                      during growth leads to an increase in wire diameter and
                      decrease in length.The second part of this work will focus
                      on the investigation of the molecular-beam-epitaxial growth
                      of the superconducting metals aluminum and niobium onto InAs
                      nanowires. Here, an impurity- and defect-free
                      semiconductor/superconductor interface is crucial in order
                      to assure a good superconducting coupling between both
                      materials. The coupling mechanism is based on the proximity
                      effect and leads to an induction of Cooper pairs into the
                      semiconductor, though only if the contacts bear a high
                      transparency. The optimal parameters to produce a smooth
                      surface as well as an impurity-free interface are
                      investigated systematically. In case of Al, the growth
                      regimes are found to depend strongly on the growth
                      temperature. In case of Nb, the growth angle and growth rate
                      have the main influence, respectively. Our investigations
                      result in the finding of growth parameters suitable for Al
                      and Nb shell deposition on InAs nanowires, enabling highly
                      transparent contacting.Finally, the quality of the Te-doped
                      Al/InAs/Al Josephson junction produced is classified via low
                      temperature measurements, provided by the group of T.
                      Schäpers. The characteristic voltage Vc extracted, suggests
                      that the interface produced, in combination with the carrier
                      incorporation, results in a comparably high figure of merit
                      Vc, i.e. a high grade junction.},
      cin          = {PGI-9},
      cid          = {I:(DE-Juel1)PGI-9-20110106},
      pnm          = {522 - Controlling Spin-Based Phenomena (POF3-522)},
      pid          = {G:(DE-HGF)POF3-522},
      typ          = {PUB:(DE-HGF)19},
      url          = {https://juser.fz-juelich.de/record/820938},
}