Effect of Electron-Phonon and Electron-Ionized Impurity Interactions on Electronic Transport in Si/Ge Superlattices

First-principles predictions of electronic transport properties of n-doped Si/Ge superlattices (SLs) revealed significant modulations with varying strain, period, and composition, indicating improvements in their thermoelectric performance. Such modulations are predicted employing the Boltzmann transport equation (BTE) framework with constant relaxation approximation (CRTA). However, recent modeling studies for bulk Si demonstrated the importance of including energy dependent relaxation times (EDRT) to improve the prediction, compared to experimental data. We compute electronic transport coefficients of n-doped Si/Ge SLs with EDRT considering both electron-phonon and electron-ionized impurity scattering mechanisms. We find that rigorous inclusion of impurity scattering mechanisms, considering the density functional theory obtained wavefunctions and anisotropic potentials improves predictions, especially at higher carrier concentrations. We observe that the strain-related modulations in transport properties are exhibited by CRTA-BTE calculations as well, including the scattering mechanisms. Our study highlights the role of different scattering mechanisms that dictate the relaxation times of strained Si/Ge SLs.