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Response of phase change memory materials to photons

Ge-Sb-Te Phase Change Materials: Optical and Electronic Properties, Structural Transformations, and Fabrication of Nanostructures Stephen G. Bishop and John R. Abelson, University of Illinois, DMR- 0412939. Response of phase change memory materials to photons.

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Response of phase change memory materials to photons

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  1. Ge-Sb-Te Phase Change Materials: Optical and Electronic Properties, Structural Transformations, and Fabrication of NanostructuresStephen G. Bishop and John R. Abelson, University of Illinois, DMR-0412939 Response of phase change memory materials to photons • Phase change chalcogenide alloys enabled rewritable optical disks (CDs and DVDs); non-volatile phase-change memories are under vigorous development by major companies to replace flash memories. • Significance / our aim: Our project generates new fundamental understanding of the phase change materials and transformation kinetics, knowledge that is also relevant for technology development. • Optically-induced modification of amorphous Ge2Sb2Te5 (GST):Many chalcogenide alloys display photo-induced metastable effects, but little has been reported on phase change materials. We showed that GST has a strong tendency to oxidize when it is illuminated by near- or above-bandgap light (Fig. 1). The oxide has lower values of (n, k) than GST. No photodarkening was detected, and we reinterpreted previous reports of photodarkening in amorphous thin films of GexSb20-xTe80 to be the result of photo-oxidation. • Optical absorption by doped phase change materials: Although doping is very widely used to tailor properties, the manner in which dopant atoms incorporate into the structure is not understood. The localized vibrational modes (LVMs) associated with a dopant provide a reasonably direct means to determine the host atom(s) to which the dopant is bonded. Our preliminary study showed that incorporating nitrogen in GeSb alloy affords a strong LVM signature (Fig. 2). • Future: Fundamental studies on the structural/thermal properties of various compositions are in progress. Fig. 1. Oxygen profile obtained by SIMS, showing that light illumination promotes oxygen incorporation. Fig. 2. Change of the optical absorption spectrum by the incorporation of nitrogen in GeSb alloy.

  2. Ge-Sb-Te Phase Change Materials: Optical and Electronic Properties, Structural Transformations, and Fabrication of NanostructuresStephen G. Bishop and John R. Abelson, University of Illinois, DMR-0412939 • Results disseminated in 2 journal papers, 1 conference proceeding, 4 conference presentations, and 3 special seminars given in other institutions • Right: Postdoctoral scientist B. Lee received the E*PCOS 07 Best Presentation Award from the European Phase Change and Ovonics Symposium held September 2007 in Switzerland • Graduate students trained in TEM/FEM, SEM, pump-probe laser technique, AFM, XPS, UPS, PL, ellipsometry, photoconductivity, Hall effect, XRD, XRR, sputtering, and evaporation • One PhD in MatSE awarded (October 2006) on the basis of work performed under this grant • Close collaboration with IBM Almaden to characterize phase change materials and pulsed-laser transformation kinetics • An undergraduate student from an under-represented group (Hispanic female) trained under a REU supplement associated with this grant (summer 2006)

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