Nonequilibrium Phonon Dynamics in a Semiconductor Quantum Well.

The dynamics of nonequilibrium phonons in heterolayers, where the carriers are quasi-two-dimensional (2D) while the equilibrium lattice excitations are those of the bulk (3D), require a new theoretical approach. We have derived a kinetic equation for the phonon one-body density matrix, and then transform it to a tractable set of equations by introducing a "phonon wavepocket" representation. Our result removes the spurious dependence on the size of the sample that results when the nonequilibrium phonons are represented in terms of decoupled 3D plane waves. Using this approach we have calculated the relaxation and the transport of carriers in both steady state and time dependent processes. The results show the importance of considering the hot phonon effect, which explains the deviation between the recent experiments and previous theoretical calculations.