Temperature and power dependence of exciton spectra in quantum dots

We employ photoluminescence spectroscopy with micrometer spatial resolution to study different types of single quantum dot structures. On dots formed by well width fluctuations in a narrow GaAs/AlGaAs quantum well, we measure linewidths around 0.1 meV at 7 K. Increasing the temperature to 50 K, a broadening up to 0.3 meV is observed. The temperature dependence varies between different dots and also between the different lines of a single dot. The energy position of the lines is remarkably stable against variation of the excitation power. On a single dot fabricated by laser induced intermixing of a GaAs/AlGaAs well an occupation of states more than 30 meV above the ground state has been achieved by quasi-resonant excitation with picosecond pulses; but still the luminescence lines hardly shift. On the other hand, a sizeable power dependence is found for a quantum dot with a lateral electric field applied by an interdigital gate structure. This shows that the very small power dependence of the line positions is related to the symmetry of the lateral confinement potential.