Tunneling transfer and energy relaxation rate of photo-excited carriers in coupled quantum wells

Tunneling transfer rate between coupled quantum wells/dots and the energy relaxation rate are studied as a function of the density of excited carriers. Both are expected to be determined by the emission rate of LO/LA phonons. It is found that if the carrier density is reduced, the tunneling escape time decreases but the energy relaxation time increases. This suggests that the emission of LO phonons produces non-equilibrium phonons which reduce the effective LO phonon emission rate, but carrier-carrier interaction enhances the scattering rate due to LA phonons. By reducing the size of the tunneling structure, i.e., in a quasi-zero-dimensional structure, the LA phonon emission rate is also reduced.