Study of size effect in silicon nanostructures using Raman spectroscopy

Abstract

The present thesis focuses on fabrication of Silicon nanostructures using Metal Induced Etching and its characterization using Raman spectroscopy. Various theoretical models have been analyzed which explain the perturbation induced due to the confinement. Experimental results were then confirmed using Scanning Electron Microscopy (SEM) and the theoretical models for the Raman line-shape of silicon nanostructures, to find out the surface morphology and the effect of quantum confinement. Comparison of two models PCM (Phonon confinement model) and MPCM (Modified Phonon Confinement Model) have been done in order to choose the suitable confinement function to account for this perturbation. Though the MPCM is not able to explain the confinement in an appropriate manner but an anomaly of broadened line shape when the size is reduced below 1 nm is observed. Furthermore, theoretical model for the Raman line shape for amorphous silicon has been proposed in order to extract the information lying under the envelope of amorphous line-shape. Also, due to the similarity between the relaxation of k0 selection rule in case of both amorphous and silicon nanostructures, a relation of size dependence on Raman shift has been proposed in line with Silicon column and Silicon sphere, which existed earlier. Considering that the amorphous silicon has no predominant crystalline structure and is a messy lattice, the size obtained from both the two models have been prescribed as the short range order in amorphous silicon in which the atoms vibrate with random frequency thus generating random phonons and showing a broadened Raman line-shape due to the overlap of spectra from each atom. Therefore a two-fold approach has been adopted to validate the short range order obtained and a close agreement between the values is observed.