Scattering of g-process longitudinal optical phonons at hotspots in silicon

Transistors with gate lengths below 100 nm generate phonon hotspots with dimensions on the order of 10 nm and peak power densities of about 50 W/μm3. This work employs molecular dynamics to investigate the impact of lattice energy density on phonon scattering at the hotspot. The hotspot studied in this work consists of longitudinal optical phonons involved in the g-type intervalley scattering of conduction electrons in silicon. A comparison of the decay modes in hotspots with high and moderate energy densities reveals that the decay mechanisms are the same but the relaxation rates differ. Scattering occurs through a three phonon process of the form LO→LA+TA, involving the zone-edge transverse acoustic modes. An increase in the energy density from a moderate value of 5 to 125 W/μm3 changes the relaxation time from 79 to 16 ps, approximately proportional to the the maximum initial amplitude of the phonons. This work improves the accuracy of the scattering rates of optical phonons and helps in advancing the electro-thermal modeling of nanotransistors