This title appears in the Scientific Report :
2015
Deposition of monocrystalline trigonal Ge_x Sb_y Te_z by Metal Organic Vapour Phase Epitaxy
Deposition of monocrystalline trigonal Ge_x Sb_y Te_z by Metal Organic Vapour Phase Epitaxy
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 chang...
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Personal Name(s): | Schuck, Martin (Corresponding author) |
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Riess, Sally / Bornhöfft, Manuel / Du, Hongchu / Mayer, Joachim / Mussler, Gregor / von der Ahe, Martina / Hardtdegen, Hilde / Grützmacher, Detlev | |
Contributing Institute: |
Mikrostrukturforschung; PGI-5 Halbleiter-Nanoelektronik; PGI-9 |
Imprint: |
2015
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Conference: | 2015 MRS Fall Meeting & Exhibit, Boston, MA (USA), 2015-11-29 - 2015-12-04 |
Document Type: |
Poster |
Research Program: |
SYnthesis and functionality of chalcogenide NAnostructures for PhaSE change memories Controlling Electron Charge-Based Phenomena |
Publikationsportal JuSER |
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. |