Electron relaxation in a double quantum dot through two-phonon processes

We theoretically study the relaxation of electron orbital states of a double quantum dot due to two-phonon processes. In particular, we calculate how the relaxation rates depend on the separation distance between the quantum dots, the strength of quantum dot confinement, and the lattice temperature. Enhancement of the relaxation rates by specific interdot distances and lattice temperatures, and the relative strength of different scattering channels are discussed. Our results show that although at low temperatures (T∼1 K) two-phonon processes are almost four orders of magnitude weaker compared to one-phonon processes in relaxing electron orbital states, at room temperature they are as important as one-phonon processes. Furthermore, at higher temperatures processes involving absorbing a phonon and emitting another one are more important than emitting or absorbing two phonons due to an interplay of the finite thermal occupation of phonon modes and the phonon density of state considerations.