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Unformatted text preview: Control of Gold Surface Diffusion on Si Nanowires Martien I. den Hertog,* ,† Jean-Luc Rouviere,* ,† Florian Dhalluin, ‡,§ Pierre J. Desre ´, § Pascal Gentile, | Pierre Ferret, § Fabrice Oehler, | and Thiery Baron ‡ Laboratoire d ′ E ´ tude des Mate ´riaux par Microscopie A V ance ´e, CEA/DRFMC, CEA-Grenoble, 17 rue des Martyrs, 38052 Grenoble Cedex 9, France, Laboratoire des Technologies de la Microe ´lectronique, CNRS UMR 5129, CEA-Grenoble 17 rue des Martyrs, 38052 Grenoble Cedex 9, France, Laboratoire de Photonique sur Silicium, CEA/LETI/DOPT, CEA-Grenoble 17 rue des Martyrs, 38052 Grenoble Cedex 9, France, and Laboratoire Silicium Nanoe ´lectronique Photonique et Structure, CEA/DRFMC, CEA-Grenoble, DRFMC, 17 rue des Martyrs, 38052 Grenoble Cedex 9, France Received December 21, 2007; Revised Manuscript Received February 21, 2008 ABSTRACT Silicon nanowires (NW) were grown by the vapor- liquid- solid mechanism using gold as the catalyst and silane as the precursor. Gold from the catalyst particle can diffuse over the wire sidewalls, resulting in gold clusters decorating the wire sidewalls. The presence or absence of gold clusters was observed either by high angle annular darkfield scanning transmission electron microscopy images or by scanning electron microscopy. We find that the gold surface diffusion can be controlled by two growth parameters, the silane partial pressure and the growth temperature, and that the wire diameter also affects gold diffusion. Gold clusters are not present on the NW side walls for high silane partial pressure, low temperature, and small NW diameters. The absence or presence of gold on the NW sidewall has an effect on the sidewall morphology. Different models are qualitatively discussed. The main physical effect governing gold diffusion seems to be the adsorption of silane on the NW sidewalls. Silicon nanowires (SiNWs) have been actively studied during the past decade, as they hold the promise of becoming key building blocks in future electronic and optoelectronic devices. They are compatible with silicon technology and could be most elegantly grown directly on their final position in a device on a wafer. However successful integration of NWs in devices will depend ultimately on the degree of control that can be obtained over structure and physical properties. One important point is whether gold is incorpo- rated at the NW either on the NW surface or in the NW volume. Indeed in many applications, for instance electric applications, it is important to have no gold incorporation, as gold is known to create deep traps. 1 However some applications, like the realization of NW web,s 2 could benefit from the presence of gold clusters on the NW surface, as it would avoid the additional deposition of gold nanoclusters at the NW surfaces. For a while, it was not clear whether gold was present on the NW surfaces. Hannon et al....
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