Lattice dynamics of silicon nanostructures

Abstract

The lattice dynamical results of silicon nanostructures with all three different degrees ofconfinement (nanoslabs, nanowires, nanodots) are systematically analysed and presentedusing an adiabatic bond charge model. In the direction of propagation of thesestructures, it is found that the phonon branches change from flat, for the smallestnanostructures, to dispersive as the nanostructure size increases. It is also notedthat in the direction of confinement all but the acoustic branches are generallyflat, with very little dispersion. The trends in the variations of the lowest andhighest confined modes at the Brillouin zone centre with nanostructure size areinvestigated. In particular, analytic expressions for the size variation of the highestmode with the dimensionality of the nanostructures have been presented. Also, ananalytic fit has been presented for the size variation of the lowest non-zero acousticmode with structure size. Finally, numerical calculations based upon Fermi’sGolden Rule formula of the dependence of the lifetime of the lowest confined modeon nanostructure size and temperature have also been obtained and discussed.