Excited-state dynamics and carrier capture in InGaAs/GaAs quantum dots

Zhang, L.; Boggess, Thomas F.; Gundogdu, K.; Flatte´, Michael E.; Deppe, D. G.; Cao, C.; Shchekin, O. B.
November 2001
Applied Physics Letters;11/12/2001, Vol. 79 Issue 20, p3320
Academic Journal
Subpicosecond time-resolved photoluminescence upconversion is used to measure the 12 K first-excited-state dynamics in large InGaAs/GaAs self-assembled quantum dots designed for 1.3 μm diode lasers. A comparison with the ground-state dynamics suggests that energy relaxation occurs in a cascade through the multiple discrete levels with an average interlevel relaxation time of ∼250 fs. Excited-state emission is observed from two distinct populations. Due to the ultrafast relaxation from the excited state to the ground state in dots containing only a single exciton, the excited-state emission is dominated by the fraction of dots that capture more than one electron–hole pair. In this case, state filling in the ground state blocks the ultrafast relaxation channel, thereby enhancing the excited-state emission. While state filling and a random capture process dictate the primary features of the excited-state emission, at low excitation levels we find that the rise time of emission from the excited state is influenced by the much denser population of singly occupied dots. © 2001 American Institute of Physics.


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