Résumé
The temperature-induced broadening of the optical spectrum is a major issue of the quantum dot optical properties. Temperature-dependent measurements have shown that the line-shape can be described by the superposition of the so-called zero-phonon line and broad side-bands extending on several meV [1]. These side-bands arise from the radiative recombination of electron-hole pairs assisted by the emission and the absorption of acoustic phonons and are quantitatively interpreted in the framework of the Huang-Rhys theory. However, within this theoretical treatment, the zero-phonon line does not show any broadening with temperature in strong contrast with the literature which shows a wide dispersion of the data on the temperature dependence of this zero-phonon line-width [2-5]. We show here that the thermal activation of the processes leading to spectral diffusion in the motional narrowing regime [6] results in a Lorentzian zero-phonon line with a width that increases linearly with temperature. This extrinsic dephasing process is studied by systematic measurements of the linewidth for single quantum dots in the motional narrowing regime, i.e. with a zero-phonon line that keeps a Lorentzian profile in the investigated range of experimental parameters. This contribution to the temperature dependence of the zero-phonon line-width relies on an interaction between acoustic phonons and carriers outside the QDs in contrast with previous models where acoustic phonons interact with carriers inside the dot. Our original model provides a unified interpretation to the published data on the temperature dependence of the zero-phonon line. [1]L. Besombes, K. Kheng, L. Marsal, and H. Mariette, Phys. Rev. B 65, 121314 (2002). [2]C. Kammerer, C. Voisin, G. Cassabois, C. Delalande, Ph. Roussignol, F. Klopf, J. P. Reithmaier, A. Forchel, and J. M. G\'{e}rard, Phys. Rev. B 66, 041306 (2002). [3]B. Urbaszek, E. J. McGhee, M. Kruger, R. J. Warburton, K. Karrai, T. Amand, B. D. Gerardot, P. M. Petroff, and J. M. Garcia, Phys. Rev. B 69, 035304 (2004). [4]G. Ortner, D. R. Yakovlev, M. Bayer, S. Rudin, T. L. Reinecke, S. Fafard, Z. Wasilewski, and A. Forchel, Phys. Rev. B 70, 201301 (2004). [5]P. Borri, W. Langbein, U. Woggon, V. Stavarache, D. Reuter, and A. D. Wieck, Phys. Rev. B 71, 115328 (2005). [6]A. Berthelot, I. Favero, G. Cassabois, C. Voisin, C. Delalande, Ph. Roussignol, R. Ferreira, and J. M. G\'{e}rard, Nature Phys. 2, 759 (2006).