Ultrafast Electron Dynamics in Coupled and Uncoupled\nHgTe Quantum Dots

In\nthis article, we study electron dynamics in HgTe quantum dots\nwith a 1.9 μm gap, a material relevant for infrared sensing\nand emission, using ultrafast spectroscopy with 35 fs time resolution.\nExperiments have been carried out at several probing photon energies\naround the gap, which allows us to follow the relaxation path of the\nphotoexcited electrons. We compare such dynamics in two kind of samples,\nHgTe quantum dots with long ligands and with short ligands, in order\nto distinguish the role of the coupling between adjacent quantum dots.\nThree main dynamics can be observed in the transient reflectivity\non both samples, with slightly different relaxation times: two fast\ndecays on the time scale of hundreds of femtoseconds and a few picoseconds,\nrespectively, followed by a slower relaxation back to the unperturbed\nvalue over hundreds of picoseconds. The two fast components are associated\nwith intraband relaxation of the photoexcited electrons within the\nconduction band, while the final relaxation path can be assigned to\nAuger relaxation mechanisms and to the slower interband exciton recombination.