Ultraviolet Raman spectra of few nanometer thick silicon-on-insulator nanofilms: Lifetime reduction of confined phonons

We show that in Si-on-insulator (SOI) nanofilms (NFs), phonon-confinement-induced longitudinal optical (LO) phonon Raman band asymmetric broadening is much weaker than thickness-inversely-proportional symmetric broadening associated with phonon lifetime reduction. We discuss the origin of the effect, determine LO phonon lifetime in SOI NFs and modify Richter-Campbell-Fauchet model describing the confined-phonon Raman band shape by taking the symmetric broadening into account. We also discuss connection of the effect with SOI NF thermal conductivity reduction.