Size dependence of Raman line-shape parameters due to confined phonons in silicon nanowires

Abstract

ABSTRACT A comparison of experimentally observed Raman scattering data with Raman line shapes, generated theoretically using a phonon confinement model, has been carried out to understand the sensitivity of different Raman spectral parameters towards the quantum confinement effect. Size-dependent variations of full width at half maximum, Raman peak position and asymmetry ratio have been analysed to establish the sensitivity of their corresponding physical counterparts (phonon lifetime and dispersion) in confined systems. The comparison has been done in three different confinement regimes, namely weakly, moderately and strongly. Proper reasoning has been assigned for such a variation after validation of the theoretical analysis with the experimental observations. A moderately confined system was created by preparing 6-nm-sized silicon nanostructures using metal-induced etching. An asymmetrically broadened and red-shifted Raman line shape was observed, which established that all the parameters get affected in a moderately confined system. Sensitivity of a given Raman spectral parameter has been shown to be used as a tool to understand the role of external perturbations in a material.