Electron-phonon interaction in individual strain-free GaAs/Al0.3Ga0.7As quantum dots

We report accurate measurements of the excitonic ground state transitions in individual, strain free, GaAs/Al0.3Ga0.7As quantum dots. We determine the spectral width and the energy of the zero-phonon line as a function of the temperature for a series of quantum dots with different sizes. In particular, the thermal broadening is well reproduced by a thermally activated process having a single activation energy (36 meV, corresponding to the GaAs LO phonon energy) independently of the dot size. Similarly, the energy of the zero-phonon line follows the GaAs gap temperature dependence irrespective of the dot size. Our findings demonstrate that (a) the exciton decoherence in quantum dots cannot be attributed to inelastic electron-phonon scattering but rather to pure dephasing processes driven by GaAs-LO phonons and (b) there is no quantum size effect on the excitonic energy renormalization with the temperature.