Long Polaron Lifetime in InAs/GaAs Self-Assembled Quantum Dots

We have investigated the polaron dynamics in $n$-doped InAs/GaAs self-assembled quantum dots by pump-probe midinfrared spectroscopy. A long $T_1$ polaron decay time is measured at both low temperature and room temperature, with values around 70 and 37 ps, respectively. The decay time decreases for energies closer to the optical phonon energy. The relaxation is explained by the strong coupling for the electron-phonon interaction and by the finite lifetime of the optical phonons. We show that, even for a large detuning of 19 meV from the LO photon energy in GaAs, the carrier relaxation remains phonon assisted.