Origin of Enhanced Thermal Resistance Near Nanoscale Hotspots: Insights from Full-Dispersion-Resolved Phonon Transport in Silicon

Phonon transport near nanoscale hotspots (NHs) critically determines heat dissipation in advanced electronic devices. The prevailing understanding is that the enhanced thermal resistance (TR) observed in NHs originates from long mean free path (MFP) phonons, whose MFPs are much larger than the hotspot size, thereby limiting their ability to recognize hotspots and transport heat effectively. In this study, we revisit this problem by employing the Boltzmann transport equation (BTE) with a full phonon dispersion model (FPDM) to capture mode-resolved velocities, scattering processes, and nonequilibrium phonon populations in silicon. The analysis demonstrates that the increase in TR near NHs is not caused by the long MFP itself but by the low specific heat of long-MFP phonons that do not scatter directly with optical modes. These phonons heat readily when energy is supplied, steepening the local temperature gradient near the NH and thereby enhancing TR. By resolving the spectral contributions to the phonon transport resistance and temperature gradients, we identify the critical role of the modal specific heat in nonlocal phonon transport. These results provide new physical insights into nanoscale thermal management and highlight the importance of spectral mode resolution in modeling heat dissipation in electronic devices.