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@INPROCEEDINGS{Schuck:280538,
      author       = {Schuck, Martin and Riess, Sally and Bornhöfft, Manuel and
                      Du, Hongchu and Mayer, Joachim and Mussler, Gregor and von
                      der Ahe, Martina and Hardtdegen, Hilde and Grützmacher,
                      Detlev},
      title        = {{D}eposition of monocrystalline trigonal ${G}e_x$ ${S}b_y$
                      ${T}e_z$ by {M}etal {O}rganic {V}apour {P}hase {E}pitaxy},
      school       = {RWTH Aachen},
      reportid     = {FZJ-2016-00306},
      year         = {2015},
      abstract     = {Phase change memory (PCM) based on chalcogenides such as
                      the Ge-Sb-Te compounds along the Sb2Te3 – GeTe
                      pseudo-binary line have been widely used for optical data
                      storage and in recent years also as nonvolatile resistive
                      memory devices. In these applications, the ultra-fast and
                      reversible phase change between the amorphous and the
                      metastable cubic crystalline phase, associated with a high
                      contrast in reflectivity and resistivity is used for data
                      storage. They are deposited in the amorphous state by atomic
                      layer deposition or physical vapour deposition (sputtering).
                      Due to the lack of applications, the thermodynamically
                      stable crystalline hexagonal phase wasnot in the centre of
                      attention up to now. However, recently superlattices of
                      highly textured hexagonal Sb2Te3 – GeTe layers have
                      received increasing interest due to an altered switching
                      mechanism with reduced switching energy.Switching is field
                      induced and occurs at the interfaces of the materials
                      between two crystalline states circumventing melting for the
                      phase change. The layered structure of monocrystalline
                      hexagonal Ge-Sb-Te inherently resembles the superlattice
                      structure with respect to atomic stacking and crystal
                      orientation to the substrate. For this reason, the
                      preparation and intense study of epitaxial, hexagonal
                      Ge-Sb-Te can be of fundamental interest for future
                      applications. In this contribution, we present the growth
                      and characterization of crystalline Ge-Sb-Te films on Si
                      (111) deposited by MOVPE. At a reactor pressure of 50 hPa
                      and growth temperatures around 450°C epitaxial films are
                      grown using nitrogen as the carrier gas to transport the
                      precursors DETe, TESb and digermane to the reactor.
                      Different partial pressures of the precursors were employed
                      to vary the film composition. The morphology of the
                      deposited material was investigated using AFM and SEM, while
                      the structure of the as-grown samples was studied by XPS,
                      XRD and TEM. The chemical composition was determined using
                      EDS.The two compositions Ge1Sb2Te4 and Ge2Sb2Te5 were
                      controllably achieved. XRD studies indicate, that the 100nm
                      thick Ge-Sb-Te is crystallized in the stable hexagonal
                      structure (P-3m1 or R-3m). TEM investigations reveal that
                      the Ge, Sb and Te atoms form building blocks, consisting of
                      7 (Ge1Sb2Te4) or 9 (Ge2Sb2Te5) alternating cation and anion
                      layers in parallel to the Si (111) substrate surface,
                      stacked along the [0001] axis. These building blocks are
                      separated by van der Waals gaps originating from hexagonal
                      Sb2Te3, where they are naturally present. The samples are
                      monocrystalline and exhibit a low amount of defects. XPS
                      reveals oxidation mainly of Ge and Sb at the surface of the
                      films. Additionally the occupation of the cation sites by Ge
                      and Sb atoms in the hexagonal lattice was investigated by
                      TEM and XPS.},
      month         = {Nov},
      date          = {2015-11-29},
      organization  = {2015 MRS Fall Meeting $\&$ Exhibit,
                       Boston, MA (USA), 29 Nov 2015 - 4 Dec
                       2015},
      cin          = {PGI-9 / PGI-5},
      cid          = {I:(DE-Juel1)PGI-9-20110106 / I:(DE-Juel1)PGI-5-20110106},
      pnm          = {521 - Controlling Electron Charge-Based Phenomena
                      (POF3-521) / SYNAPSE - SYnthesis and functionality of
                      chalcogenide NAnostructures for PhaSE change memories
                      (310339)},
      pid          = {G:(DE-HGF)POF3-521 / G:(EU-Grant)310339},
      typ          = {PUB:(DE-HGF)24},
      url          = {https://juser.fz-juelich.de/record/280538},
}