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@PHDTHESIS{SchulteBraucks:844750,
      author       = {Schulte-Braucks, Christian},
      title        = {{I}nvestigation of {G}e{S}n as {N}ovel {G}roup {IV}
                      {S}emiconductor for {E}lectronic {A}pplications},
      volume       = {168},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2018-02130},
      isbn         = {978-3-95806-312-9},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {XX, 165, XII S.},
      year         = {2018},
      note         = {RWTH Aachen, Diss., 2017},
      abstract     = {Within the last few years single crystalline GeSn
                      semiconductor alloys aroused significant scientific
                      interest, especially since 2015, when GeSn with sufficiently
                      high Sn content and crystalline quality was demonstrated as
                      fundamentally direct bandgap group IV semiconductor. While
                      enhanced optical properties are evident for direct bandgap
                      materials compared to the fundamentally indirect Ge and Si
                      group IV semiconductors, also enhanced electrical properties
                      like increased carrier mobilities and enhanced band-to-band
                      tunneling are expected for direct bandgap GeSn which are
                      beneficial for metal-oxide semiconductor transistors and
                      tunnel field-effect transistors, respectively. The novel
                      GeSn semiconductor alloys thereby manifests a fascinating
                      emerging material system allowing a wide scope to study its
                      fundamental physical, electrical, optical and chemical
                      properties. On the other hand the novelty of the material
                      system demands the re-development or modification and
                      verification of all steps necessary to build GeSn based
                      semiconductor devices. A comprehensive study is presented,
                      focusing on the electrical properties of GeSn, their
                      dependence on Sn content and possible applications in novel
                      electronic devices. The building blocks of field-effect
                      transistors are studied individually. GeSn surface
                      composition and manipulation are investigated $\textit{via}$
                      X-ray photoemission spectroscopy to study pre-high-$\kappa$
                      deposition cleaning and highly selective Ge/GeSn etching
                      processes. NiGeSn alloys for the use as electrical contacts
                      of GeSn devices are structurally and electrically
                      characterized using X-ray diffraction, transmission electron
                      microscopy and temperature dependent current voltage
                      measurements, respectively. Schottky barrier height, sheet
                      resistance and specific contact resistivity are extracted.
                      The modification of the NiGeSn/GeSn Schottky barrier height
                      $\textit{via}$ dopant segregation is demonstrated for the
                      first time. Schottky-barrier heights as low as 0.06 eV are
                      observed. As a next module metal-oxide-semiconductor
                      capacitors are comprehensively studied. High-$\kappa$/GeSn
                      interface trap densities are extracted for a wide range Sn
                      contents. The focus is placed on the effect of the
                      electronic band structure of GeSn on the capacitance voltage
                      characteristics. Fundamental trends demonstrating the
                      correlation of Sn-induced bandgap shrinkage and minority
                      carrier response are observed. Furthermore a maximum
                      capacitance of approx. 3 $\mu$F/cm$^{2}$ is achieved. As a
                      step towards GeSn based tunnel field-effect transistors,
                      Esaki diodes (tunnel diodes) are fabricated and electrically
                      characterized. Negative differential resistance with a
                      peak-to-valley current ratio of 2.3 is observed as an
                      experimental proof of band-to-band tunneling. Enhanced
                      band-to-band tunneling rates are observed in
                      Ge$_{0.89}$Sn$_{0.11}$ $\textit{p-i-n}$ diodes compared to
                      Ge taking advantage of the low and direct bandgap. These
                      studies lead to the realization of vertical heterojunction
                      Ge$_{0.93}$Sn$_{0.07}$/Ge tunnel field-effect transistors.
                      An extensive analysis is provided identifying the various
                      contributions to the overall transistor current,
                      particularly band-to-band tunneling and trap-assisted
                      tunneling. Finally, Hall measurements are presented, showing
                      enhanced electron mobilities in direct bandgap GeSn as
                      compared to Ge. With up to 4600 cm$^{2}$/Vs this marks the
                      highest bulk electron mobilities at the respective doping
                      level of 2.9 · 10$^{17}$ cm$^{−3}$ in a group IV
                      semiconductor so far.},
      cin          = {PGI-9},
      cid          = {I:(DE-Juel1)PGI-9-20110106},
      pnm          = {521 - Controlling Electron Charge-Based Phenomena
                      (POF3-521)},
      pid          = {G:(DE-HGF)POF3-521},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:0001-2018050980},
      url          = {https://juser.fz-juelich.de/record/844750},
}