Electron-phonon coupling in polycrystalline silicon

WX Liu and X Xiang and YG Zhou, PHYSICAL REVIEW B, 112, 155301 (2025).

DOI: 10.1103/b1ry-rnqz

Here, the electron-phonon coupling (EPC) in polycrystalline nanostructures is systematically studied using Langevin dynamics simulations with spatial correlations. The EPC constant in polycrystalline nanostructures is found to be larger than that in their single-crystalline counterparts and increases with the decrease of the grain size and carriers' concentration. The EPC constant for polycrystalline silicon with a grain size of similar to 5 nm and a carriers' concentration of 6.9 x 1021 cm-3 is improved from its bulk counterpart value of similar to 1.44 x 1017 W/m3 K to similar to 1.84 x 1017 W/m3 K. The temperature of phonon modes in polycrystals therefore increases faster than that in the corresponding single crystals. Our spectral analysis shows that additional high-frequency phonon modes are activated in polycrystals and therefore provide more possible coupling channels for electrons. Meanwhile, the overall temperature of optical phonon modes is observed to increase faster than that of acoustic phonon modes in both polycrystals and single crystals. Our calculated scattering rates show that the scattering rate between optical phonons and electrons is generally larger than that between acoustic phonons and electrons. The scattering rate between optical phonons and acoustic phonons is much larger than that between phonons and electrons. This indicates that the energy of hot electrons is transferred to optical phonon modes, and acoustic phonon modes gain thermal energy from optical phonon modes through their interactions. As a result, the temperature of optical phonon modes increases faster than that of acoustic phonon modes in the systems. Further increase of carriers' concentration can increase the scattering rate between electrons and phonons, and thus increase the EPC constant. Our study here highlights the influence of grain boundaries and carriers' concentration on EPC in polycrystalline nanostructures, which benefits future carrier dynamics investigations.

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