Stimulated decay of nonselectively pumped optical phonons in GaAs

We have considered the processes determining the steady-state population of longitudinal optical (LO) phonons being intensively produced in GaAs by electrons optically excited or accelerated in strong external electric field. The emitted LO phonons pass their energy to acoustic phonon systems through anharmonic decay into longitudinal acoustic (LA) phonons. The latter emerge as almost monoenergetic and concentrated in a narrow layer in the reciprocal space. Had the occupation numbers of k states within this layer grown to unity, the decay process would have become stimulated, effectively desolating the built-in LO states and giving rise to various nonlinear phenomena. We show that this is actually the case by tracing LA phonon kinetics and calculating the number of phonons in each k state available for feedback. The results obtained substantially clarify the physical picture of energy transfer processes mediating heat removal in GaAs.