Optical transitions and carrier relaxation in self assembled InAs/GaAs quantum dots

Abstract

We present experimental results concerning optical transitions and carrier dynamics (capture and relaxation) in self assembled InAs/GaAs quantum dot structures grown by metalorganic vapor phase epitaxy. Photoluminescence (PL) measurements at high excitation level reveal optical transitions above the ground state emission. These transitions are found to originate from occupied hole states by solving the quantum dot eigenvalue problem. Time-resolved studies after non-resonant pulse excitation exhibit a relaxation ladder of the excited carriers from the GaAs barrier down to the ground state of the quantum dots. From both the continuous-wave measurements and the PL-decay curves we conclude that the carrier relaxation at non-resonant excitation is mediated by Coulomb interaction (Auger effect). PL-decay curves after resonant pulse excitation reveal a longer rise time compared to non-resonant excitation which is a clear indication of a relaxation bottleneck inside the quantum dots. We interpret the rise time (≊ 400 ps) in this case to originate from relaxation via scattering by acoustic phonons. The PL-decay time of the ground state emission ≊700 ps is interpreted as the excitonic lifetime of the quantum dot.

A Theoretical Study of Structural Disorder and Photoluminescence Linewidth in InGaAs/GaAs Self Assembled Quantum Dots

“…We find that the effective gaps range from 0.954 to 1.2 eV as the height changes from 85 to 55 A. The preferred size has a peak energy of-1.04 eV, which agrees well with the experimental PL results [14]. The electronic spectrum for different dot sizes is shown in figure 4.…”

Quantum dot materials for terahertz generation applications

“…Photoluminescence recombination measurements www.lpr-journal.org indicate a shorter recombination time from the excited states (ES) as compared to the GS. Non-radiative relaxation processes that result from the Auger effect [25] and step-wise ("intra-dot") relaxation of excitons through subsequent QD energy states are dependent on both the available intraband relaxation channels and phonon interactions [26]. The difference between carrier capture and carrier relaxation in this case is defined by whether photocarriers are considered as mobile or not mobile.…”

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“…Therefore, the excited carriers in the WLs and the spacer layers lead to the transfer of an impaired hole into the QDs (Adler et al, 1996). In the lower temperature region, lateral coupling-like behaviour arises from the hole injection from the spacer layers.…”