title: Facet-Selective Nucleation and Conformal Epitaxy of Ge Shells on Si Nanowires.
abstract: Knowledge of nanoscale heteroepitaxy is continually evolving as advances in material synthesis reveal new mechanisms that have not been theoretically predicted and are different than what is known about planar structures. In addition to a wide range of potential applications, core/shell nanowire structures offer a useful template to investigate heteroepitaxy at the atomistic scale. We show that the growth of a Ge shell on a Si core can be tuned from the theoretically predicted island growth mode to a conformal, crystalline, and smooth shell by careful adjustment of growth parameters in a narrow growth window that has not been explored before. In the latter growth mode, Ge adatoms preferentially nucleate islands on the {113} facets of the Si core, which outgrow over the {220} facets. Islands on the low-energy {111} facets appear to have a nucleation delay compared to the {113} islands; however, they eventually coalesce to form a crystalline conformal shell. Synthesis of epitaxial and conformal Si/Ge/Si core/multishell structures enables us to fabricate unique cylindrical ring nanowire field-effect transistors, which we demonstrate to have steeper on/off characteristics than conventional core/shell nanowire transistors.
authors.affiliation: Center for Integrated Nanotechnologies, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.|Department of Electrical and Computer Engineering, University of California San Diego , La Jolla, California 92093, United States.
authors.forename: Binh-Minh
authors.initials: BM
authors.lastname: Nguyen
authors.affiliation: Center for Integrated Nanotechnologies, Sandia National Laboratories , Albuquerque, New Mexico 87185, United States.
authors.forename: Brian
authors.initials: B
authors.lastname: Swartzentruber
authors.affiliation: Department of Electrical and Computer Engineering, University of California San Diego , La Jolla, California 92093, United States.
authors.forename: Yun Goo
authors.initials: YG
authors.lastname: Ro
authors.affiliation: Center for Integrated Nanotechnologies, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.|Department of Electrical and Computer Engineering, University of California San Diego , La Jolla, California 92093, United States.|Materials Science Program, University of California San Diego , La Jolla, California 92093, United States.
authors.forename: Shadi A
authors.initials: SA
authors.lastname: Dayeh
keywords: FET; Ge; Si; core/shell; facet; misfit dislocation; nanowire; nucleation