Anharmonic decay of non-equilibrium intervalley phonons in silicon

We study phonons produced by transitions between the equivalent X valleys in silicon. We use the Monte Carlo method first to select stochastically the time between phonon collisions, and then to select a final-state pair of phonons from the probability distribution for anharmonic decay. Our results show that intervalley phonons decay into one near-equilibrium transverse acoustic phonon and another intermediate longitudinal phonon either on the acoustic or optical branch. This second phonon has energies between 40 and 50 meV and undergoes another decay before turning into a pair of near-equilibrium transverse acoustic phonons, presenting an additional potential bottleneck.