Modeling Grain Boundary Scattering and Thermal Conductivity of Polysilicon Using an Effective Medium Approach

This work develops a new model for calculating the thermal conductivity of polycrystalline silicon using an effective medium approach which discretizes the contribution to thermal conductivity into that of the grain and grain boundary regions. While the Boltzmann transport equation under the relaxation time approximation is used to model the grain thermal conductivity, a lower limit thermal conductivity model for disordered layers is applied in order to more accurately treat phonon scattering in the grain boundary regions, which simultaneously removes the need for fitting parameters frequently used in the traditional formation of grain boundary scattering times. The contributions of the grain and grain boundary regions are then combined using an effective medium approach to compute the total thermal conductivity. The model is compared to experimental data from literature for both undoped and doped polycrystalline silicon films. In both cases, the new model captures the correct temperature dependent trend and demonstrates good agreement with experimental thermal conductivity data from 20 to 300K.