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@PHDTHESIS{Tromm:862553,
      author       = {Tromm, Thomas Carl Ulrich},
      title        = {{H}igh-k rare-earth oxides on {G}a{N} and ferroelectric
                      properties of hafnia based thin films},
      school       = {RWTH Aachen University},
      type         = {Dissertation},
      reportid     = {FZJ-2019-02847},
      pages        = {133 p.},
      year         = {2019},
      note         = {Dissertation, RWTH Aachen University, 2014},
      abstract     = {The continuous improvement of the transistors is the basis
                      for the increase of computing power. For enhanced
                      metal-oxide-semiconductor (MOS)
                      field-effect-transistors(FETs) and other devices suitable
                      gate dielectrics are required, that exhibit a high relative
                      permittivity, good insulating properties like a large band
                      gap, and a goodlayer quality. Additionally, new device
                      structures like negative capacitance FET (NCFET) are
                      developed.In this thesis the ternary rare-earth oxides
                      GdScO3 (GSO), LaLuO3 (LLO) and SmScO3 (SSO) are grown on GaN
                      by pulsed laser deposition (PLD). Those oxidesreveal a
                      hexagonal phase, that has been discovered few years ago. The
                      oxides have a large lattice mismatch to the GaN and are not
                      at thermodynamic equilibrium,according to ab-initio
                      calculations. The hexagonal ternary rare-earth oxides reveal
                      a permittivity of 30 (GSO) and of 32 (LLO) and a bandgap
                      above 5 eV. To understandthe growth mechanism of the
                      rare-earth oxides, the layer and especially the interface
                      are investigated. First of all hexagonal GSO reveals a
                      decomposition of Scand Gd at the interface, so that it
                      exhibits twice as much Sc than Gd, which reduces the length
                      of the in-plane axis of the GSO and subsequently the lattice
                      mismatch.Secondly, the grains are tilted in-plane, revealing
                      a fibre texture with the c-axis as fibre axis perpendicular
                      to the interface. Thirdly, the distance of the lattice
                      planesat the interface is enhanced, revealing a distance of
                      3.1 Å. The SSO also reveals a fibre texture and an enhanced
                      interface distance, thought the decomposition of theSm and
                      the Sc occurs in places. The hexagonal LLO reveals a fibre
                      texture and a small decomposition.For a novel NCFET a
                      ferroelectric is placed in between the gate metal and the
                      oxide of a MOSFET. The ferroelectric should exhibit a
                      negative capacitance and inthis way cause a voltage
                      amplification, resulting in a subthreshold slope (SS) below
                      60 mV/dec. PLD grown ferroelectric HfO2 with $5\%$ Gd and
                      HfO2 with $5\%$ Lu(HfLuO) reveal a remanent polarization of
                      12 μC/cm2, while the HfO2 with $5\%$ Y, grown by atomic
                      layer deposition, reveals one of 20 μC/cm2 and a steeper
                      hysteresis.HfLuO exhibits a pinched hysteresis at the
                      initial state, if the sample is annealed at 500 °C, which
                      could be related to an antiferroelectric phase. At an
                      annealingtemperature of 700 °C the HfLuO layer becomes
                      ferroelectric.},
      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)11},
      url          = {https://juser.fz-juelich.de/record/862553},
}