Phonon scattering in silicon films with thickness of order 100 nm

Although progress has been made in the ab initio simulation of lattice dynamics in semiconducting crystals, information about the relaxation of nonequilibrium lattice vibrations remains incomplete. This work studies the relaxation times of room-temperature thermal phonons through measurements of thermal conduction along monocrystalline silicon films of thickness down to 74 nm. A repetitive oxidation and etching process ensures that the purity and crystalline quality of the films are comparable with those of bulk samples. Phonon-interface scattering reduces the thermal conductivity by up to 50% at room temperature. The data indicate that the effective mean-free path of the dominant phonons at room temperature is close to 300 nm and thus much longer than the value of 43 nm predicted when phonon dispersion is neglected. This study indicates that a broad variety of lattice transport characteristics for bulk silicon can be obtained through measurements on carefully prepared silicon nanostructures. The present data are also valuable for the thermal simulation of silicon-on-insulator (SOI) transistors.