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Heat and charge transport in bulk semiconductors with interstitial defects

Link to journal

Vitaly S. Proshchenko, Pratik P. Dholabhai, Tyler C. Sterling, and Sanghamitra Neogi,
Phys. Rev. B, 99, 014207 (2019)

Atomistic and first principles study of the variability of heat and charge transport properties of bulk silicon, in the presence of randomly distributed interstitial defects (Si, Ge, C, and Li).

Interstitial defects are inevitably present in doped semiconductors that enable modern-day electronic, optoelectronic, or thermoelectric technologies. Understanding the stability of interstitials and their bonding mechanisms in the silicon lattice was accomplished only recently with the advent of first-principles modeling techniques, supported by powerful experimental methods. However, much less attention has been paid to the effect of different naturally occurring interstitials on the thermal and electrical properties of silicon. In this work, we present a systematic study of the variability of heat and charge transport properties of bulk silicon, in the presence of randomly distributed interstitial defects (Si, Ge, C, and Li). We find through atomistic lattice dynamics and molecular dynamics studies that interstitial defects scatter heat-carrying phonons to suppress thermal transport-1.56% of randomly distributed Ge and Li interstitials reduce the thermal conductivity of silicon by ~30 and 34 times, respectively. Using first-principles density functional theory and semiclassical Boltzmann transport theory, we compute electronic transport coefficients of bulk Si with 1.56% neutral Ge, C, Si, and Li interstitials, in energetically favorable hexagonal, tetrahedral, split-interstitial, and bond-centered sites. We demonstrate that hexagonal-Si and hexagonal-Ge interstitials minimally impact charge transport. As an illustration of the relevance of this work for practical applications, we predict the thermoelectric property of an experimentally realizable bulk Si sample that contains Ge interstitials in different symmetry sites. Our research establishes a direct relationship between the variability of structures dictated by fabrication processes and heat and charge transport properties of silicon. The relationship provides guidance to accurately estimate performance of Si-based materials for various technological applications.