Two-color femtosecond spectroscopy of blue-shifted InAs/AlGaAs quantum dots

Ultrafast relaxation phenomena in self-organized InAs/AlGaAs quantum dots with ground state transition energies of 1.42 eV are analyzed with different methods of femtosecond spectroscopy. A time-correlated luminescence experiment of an ensemble of InAs islands reveals a picosecond relaxation mechanism of carriers within the quantum dots. Moreover, modifications of the quantum dot properties due to excitation of the surrounding wetting layer is found. Employing a shadow-mask technique, a structure containing only a few zero-dimensional objects is studied. Selectively creating electron-hole pairs in excited states of approximately ten quantum dots, we observe characteristic line shifts of their ground state absorption in a two-color femtosecond transmission experiment. This finding demonstrates the feasibility of ultrafast studies of single self-assembled quantum dots.