Evaluation of overall mechanical properties of polysilicon films, taking into account grain boundary effects

In this study we investigate the effects of polycrystal morphology on the overall properties of polysilicon, taking into account grain boundary effects. Focusing on two-dimensional representative volume elements (RVEs) of textured films, we numerically generate digital polycrystal morphologies through Voronoi tessellations, and assume the in-plane orientation of the crystal lattice of silicon grains to be randomly distributed. On the contrary, we assume isotropic silicon morphology inside grain boundaries. First, we describe the constitutive relations used in the analysis. We describe different types of symmetry in fcc structured brittle materials especially silicon. Second, we provide a simple model containing two square grains with grain boundary in between. The aim of this simple model is to change crystal orientation of each individual grain and to investigate the effects on the overall mechanical properties of the silicon aggregate. Third, we provide a numerical homogenization technique to estimate the overall in-plane elastic moduli of the polysilicon film, while grain boundary thickness has been increased gradually, and compare the outcomes with standard Voigt and Reuss bounds. Through this comparison, we furnish a way to also estimate the size of the RVE to get effective results regarding different parameters changes such as: number of regularization of grain shape, and thickness of grain boundary. Also, we investigate the effect of changing polysilicon morphology on the scattering of the overall elastic properties of two randomly tessellated specimens. We compare two sets of tessellations in order to clarify the fluctuation arising from the stochastic nature of the crystal lattice orientation.