Modification of the lattice thermal conductivity in silicon quantum wires due to spatial confinement of acoustic phonons

Lattice thermal conductivity in silicon quantum wires is theoretically inve stigated. The bulk of heat in silicon structures is carried by acoustic pho nons within a small region in the first Brillouin zone. Our formalism rigor ously takes into account modification of these acoustic phonon modes and ph onon group velocities in free- and clamped-surface wires due to spatial con finement. From our numerical results, we predict a significant decrease (mo re than an order of magnitude) of the lattice thermal conductivity in cylin drical quantum wires with diameter D = 200 Angstrom. The decrease is about two times stronger in quantum wires than in quantum wells of corresponding dimensions. Our theoretical results are in qualitative agreement with exper imentally observed drop of the lattice thermal conductivity in silicon low- dimensional structures. (C) 1999 Academic Press.