Nonequilibrium optical phonon generation by steady-state electron transport in quantum-cascade lasers

Observation of the nonequilibrium optical phonons population associated with electron transport in quantum-cascade lasers is reported. The phonon occupation number was measured in the range 75–280 K by using a combination of microprobe photoluminescence and Stokes/anti-Stokes Raman spectroscopy. The excess phonon population is observed to decrease as the lattice temperature increases. From the nonequilibrium phonon population, we extracted interface phonon lifetimes of 5 ps at 75 K and 2 ps at 280 K.