Temperature dependent phonon-assisted hot carrier (including electron and hole) relaxation dynamics in PbSe quantum dot is studied within ab initio density functional theory. The electronic structure is first calculated, showing that the electronic states are denser than holes. Fourier transforms of the time resolved energy levels show that the hot carriers couple to both acoustic and optical phonons. At higher temperature, more phonon modes in the high frequency range participate in the relaxation process due to their increased occupation number. The phonon-assisted hot carrier decay dynamics is predicted using non-adiabatic molecular dynamics, and the calculated relaxation rates clearly shows a temperature-activation behavior. The complex temperature dependence is attributed to the combined effects of the phonon occupation number and thermal expansion. Comparing the simulation results with experiments, we suggest that the multiphonon relaxation channel is efficient at high temperature, while the Auger-like process may dominate the relaxation at low temperature. This combined mechanism can explain the weak temperature dependence at low temperature and stronger temperature dependence at higher temperature.
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