Excited states and multi-exciton complexes in single CdTe quantum dots

We report on an optical study of excited states in single CdTe quantum dots (QDs). Micro-photoluminescence excitation (muPLE) measurements first reveal the existence of confined excited states as well as absorption of delocalized states in the CdTe layer. Up to two confined excited states are clearly observed in some of the dots. Power-dependent micro-photoluminescence (muPL) is then used to study the multiexciton complexes resulting from the occupation of excited states. The optical spectra features depend on both the depth of the confinement potential and on the symmetry of the dot. A simplification of the emission spectra structure can be found for a symmetric dot, showing clear filling of QD discrete levels. This is attributed to the fulfilling of the high-symmetry condition that leads to cancellation of inter-particle interactions in the multiple-particle Hamiltonian.