Photoluminescence properties of partially phase separated silicon nitride films

Abstract

Photoluminescence properties of partially phase separated amorphous silicon nitride films, lying in between homogeneous materials and composites embedding pure Si nanoparticles, have been investigated. With excitation energy above the Tauc gap, the emission band systematically blue-shifts and broadens with decreasing silicon content, suggesting tail to tail recombination as the prevailing luminescence mechanism. With subgap excitation, the response is instead peaked at 1.7 eV independently of the stoichiometry, likely as an effect of the spatial fluctuations of the gap. In this case, excitation and emission selectively occur in the Si rich domains within the material, and direct band to band recombination is proposed as the possible dominant process. Another effect of the nonuniform material composition is likely the unusual S-shaped evolution of the integrated photoluminescence intensity versus temperature observed for the sample richest in Si. This behavior has been described with a phenomenological model including two thermally activated nonradiative processes and one electron trap energy level.