TEMPERATURE AND POWER DEPENDENCE OF EXCITON SPECTRA IN QUANTUM DOTS

We employ photoluminescence spectroscopy with micrometer spatial resol ution to study different types of single quantum dot structures. On do ts formed by well width fluctuations in a narrow GaAs/AlGaAs quantum w ell, we measure linewidths around 0.1 meV at 7 K. Increasing the tempe rature to 50 K, a broadening up to 0.3 meV is observed. The temperatur e dependence varies be tween different dots and also between the diffe rent lines of a single dot. The energy position of the lines is remark ably stable against variation of the excitation power. On a single dot fabricated by laser induced intermixing of a GaAs/AlGaAs well, an occ upation of states more than 30 meV above the ground state has been ach ieved by quasi-resonant excitation with picosecond pulses; but still t he luminescence lines hardly shift. On the other hand, a sizeable powe r dependence is found for a quantum dot with a lateral electric field applied by an interdigital gate structure. This shows that the very sm all power dependence of the line positions is related to tile symmetry of the lateral confinement potential.