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@INPROCEEDINGS{Schuck:154844,
      author       = {Schuck, Martin and Riess, Sally and Schreiber, Marcel and
                      Mussler, Gregor and Mennicken, Max and Grützmacher, Detlev
                      and Hardtdegen, Hilde},
      title        = {{MOVPE} of crystalline {G}e1{S}b2{T}e4 ({GST})},
      school       = {RWTH Aachen},
      reportid     = {FZJ-2014-04107},
      year         = {2014},
      abstract     = {Chalcogenide phase change materials show significant
                      promise on the road to an ideal memory. Ge-Sb-Te alloys
                      (GST) are considered to be one of the most suitable
                      compounds for this application and are already widely used
                      as non-volatile phase change memory in optical data storage
                      and in first PRAM (Phase-change Random Access Memory)
                      devices today [1, 2]. The reason is the rapid and reversible
                      change between its amorphous and crystalline phase with
                      orders of magnitude differences in reflectivity and
                      electrical resistivity. To this end the compounds along the
                      Sb2Te3 - GeTe pseudobinary line are the most widely used.
                      Nearly all GST layers are deposited in the amorphous phase
                      by sputtering. However, if nanostructures are to be achieved
                      without (reactive ion) etching and its detrimental side
                      effects, a bottom-up approach of single crystalline material
                      is more appropriate [3]. Also a CMOS compatible approach
                      should be adopted, which should be free of catalysts such as
                      Au. Starting point for the investigations are growth
                      conditions in MOVPE at which flat homogeneous coalesced
                      crystalline layers are deposited with only one composition.
                      A special challenge is the incorporation of Germanium. In
                      future the conditions are to be applied to selective area
                      growth of nanostructures such as nanowires, with which a
                      high scalability of structures can be ensured.Deposition was
                      performed in a horizontal low-pressure MOCVD reactor on 2”
                      Si (111) wafers, which were deoxidized by hydrofluoric acid
                      prior to the growth. Pure N2 carrier gas transported the
                      source compounds triethylantimony (TESb) and
                      diethyltelluride (DETe) as metal-organic precursors into the
                      reactor. The hydride digermane (Ge2H6) was chosen as the as
                      the Ge source. The partial pressures of the sources (Ge2H6:
                      1.46 x 10-2 mbar, TESb: 4.77 x 10-3 mbar, DETe: 1.32 x 10-1
                      mbar), the total gas flow of 2500 ml/min and the growth time
                      of 60 min were held constant. The reactor pressure was
                      varied between 50 mbar and 350 mbar and growth temperatures
                      in the range of 425°C up to 475°C. The influence of an
                      in-situ treatment of the substrate at growth-temperature
                      prior to deposition was investigated. To this end the
                      substrates were pre-treated with various sources and source
                      combinations for 1 min to 15 min. The influence of a
                      stabilizing pause between the in-situ pre-treatment and the
                      successive GST growth was also studied. The deposited
                      material was characterized by means of scanning electron
                      microscopy, Raman spectroscopy, atomic force microscopy,
                      energy dispersive X-Ray spectroscopy and X-Ray Diffraction
                      to determine topography, crystal structure and composition
                      of the grown layers.It was found that a lower reactor
                      pressure led to a more pronounced growth of flat layers. At
                      lower pressures, the growth temperature needed to be
                      increased slightly on account of the poorer decomposition of
                      the sources. While at a reactor pressure of 250 mbar and T =
                      420°C the deposited material consists of triangularly
                      shaped crystals with a height of about 1 µm, the samples
                      grown at 50 mbar consisted of nearly coalesced layers of GST
                      with a height around 100 nm and flat surfaces (Figure 1).
                      The samples deposited at 50 mbar exhibit a high
                      crystallinity. Their structure was determined to be
                      Ge1Sb2Te4, crystallized in the hexagonal phase (hcp) (Figure
                      2).An in-situ deposition of germanium in an antimony
                      atmosphere prior to the growth of GST promotes the growth of
                      flat layers by improving the coverage of the substrate
                      without disturbing the crystallinity or composition on the
                      Si (111) substrate. This is in accordance to the results
                      found for the growth of GST on SiN and SiO2 surfaces [4].},
      month         = {Jul},
      date          = {2014-07-13},
      organization  = {17th International Conference on
                       Metalorganic Vapor Phase Epitaxy,
                       Lausanne (Switzerland), 13 Jul 2014 -
                       18 Jul 2014},
      subtyp        = {Other},
      cin          = {PGI-9},
      cid          = {I:(DE-Juel1)PGI-9-20110106},
      pnm          = {421 - Frontiers of charge based Electronics (POF2-421) /
                      SYNAPSE - SYnthesis and functionality of chalcogenide
                      NAnostructures for PhaSE change memories (310339)},
      pid          = {G:(DE-HGF)POF2-421 / G:(EU-Grant)310339},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/154844},
}