Matrix Density Effect on Morphology of Germanium Nanocrystals Embedded in Silicon Dioxide Thin Films
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Matrix Density Effect on Morphology of Germanium Nanocrystals Embedded in Silicon Dioxide Thin Films Arif S. Alagoz1, 2, Mustafa F. Genisel3, 4, Steinar Foss5, Terje G. Finstad5, Rasit Turan2 1
Department of Applied Science, University of Arkansas at Little Rock, Little Rock, AR, U.S.A Department of Physics, Middle East Technical University, Ankara, Turkey. 3 Department of Chemistry, Middle East Technical University, Ankara, Turkey. 4 Department of Chemistry, Bilkent University, Ankara, Turkey. 5 Department of Physics, University of Oslo, Oslo, Norway. 2
ABSTRACT Flash type electronic memories are the preferred format in code storage at complex programs running on fast processors and larger media files in portable electronics due to fast write/read operations, long rewrite life, high density and low cost of fabrication. Scaling limitations of top-down fabrication approaches can be overcome in next generation flash memories by replacing continuous floating gate with array of nanocrystals. Germanium (Ge) is a good candidate for nanocrystal based flash memories due its small band gap. In this work, we present effect of silicon dioxide (SiO2) host matrix density on Ge nanocrystals morphology. Low density Ge+SiO2 layers are deposited between high density SiO2 layers by using off-angle magnetron sputter deposition. After high temperature post-annealing, faceted and elongated Ge nanocrystals formation is observed in low density layers. Effects of Ge concentration and annealing temperature on nanocrystal morphology and mean size were investigated by using transmission electron microscopy. Positive correlation between stress development and nanocrystal size is observed at Raman spectroscopy measurements. We concluded that nonuniform stress distribution on nanocrystals during growth is responsible from faceted and elongated nanocrystal morphology. INTRODUCTION One of the main issues in information technology (IT) is the storage of digital information. Nanocrystal based new generation flash memories are promising to follow Moore’s law and overcome scaling limitations with higher operation performance. Intensive researches have been focused especially on germanium nanocrystal [1-9] due to its fabrication compatibility with current complementary metal oxide semiconductor (CMOS) technology and small band gap, providing short writing/erasing and long retention time [2,3]. Ion implantation [4], chemical vapor deposition [5], laser ablation deposition [6] and magnetron sputter deposition [7-9] have been widely used techniques to fabricate germanium nanocrystals embedded in a various host matrix. In this study, we fabricated germanium nanocrystals embedded in silicon dioxide host matrix by off-angle magnetron sputter deposition and high temperature post annealing. We sandwiched low density Ge+SiO2 layers between higher density SiO2 layers. After post annealing, we observed non-spherical and faceted Ge nanocrystals in low density Ge+SiO2 layers. TEM measurements showed that atomic Ge concentration, annealing temperature and
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