Quantum confinement effects in silicon nanocrystals produced by laser-induced etching and cw laser annealing

A comparative study of quantum confinement of electrons and phonons in silicon nanocrystals produced by laser-induced etching on a silicon ( Si) substrate and continuous wave ( cw) laser-induced crystallization in a-Si: H film on a quartz substrate is presented here. Raman line shapes of optical phonons confined in Si nanocrystals were utilized using a phenomenological phonon-confinement model. It is appropriately modified by incorporating a Gaussian distribution of sizes for two-dimensional ( columnar) and three-dimensional ( spherical) confinement parameters for laser-induced etching and cw laser-induced crystallization processes, respectively. The calculated mean crystallite sizes were in consonance with those calculated from the bond-polarizability model. Confinement effects were found to be more prominent in Si nanocrystals prepared by laser-induced crystallization in comparison to laser-etched Si. Photoluminescence spectra of both the samples were also utilized to study the dimensionality aspect of nanocrystals.