Correlation between microstructural and optical properties of silicon thin films grown onto porous alumina by plasma–enhanced CVD method

Abstract

The silicon nanocrystals (Si NCs) are fabricated on a porous alumina (PAl) matrix by PECVD technique at different deposition time (dt) in order to produce PAlSi thin films with a high crystallinity. In this work, we report a correlation between microstructural and optical characterizations of PAlSi alloy in term of volumic Si NCs fraction and mainly the Si NCs sizes. The morphology and structure of the samples were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X–ray spectroscopy (EDX), X–Ray Diffraction (XRD) technique, and Raman spectroscopy. Optical properties of the microstructure were studied using spectroscopic ellipsometry (SE) data. Based on the SE data, an appropriate optical model is used to describe the PAlSi content with various volumic fraction of Si NCs. Bruggeman effective medium approximation and Forouhi-Bloomer models are used to analyze the effects of the volumic crystalline Si fraction on the optical properties of PAlSi, such as the refractive index (n), extinction coefficient (k) and energy band gap (Eg), as well as the dielectric functions. We show that the crystallization process is strongly dependent on the degree or the volumetric fractions of Si NCs embedded in a PAl matrix.