(a) 2 μm × 2 μm topographical AFM image, (b) 2 μm × 2 μm angle-mapped AFM image, in which the gray scale is related to the local surface slope, and (c) histogram of the QD height distribution of uncapped InAs/GaAs QDs.
Experimental LAADF image of InAs QDs capped with In0.30Ga0.70As UCL.
Normalized PL spectra of QD structures acquired at 13 K under low excitation power density (black dots) and high excitation power density (purple line); the nominal In content in the UCL is: (a) x = 0, (b) x = 0.10, (c) x = 0.20, (d) x = 0.30. PL spectra at low excitation power density are fitted with a double-gaussian profile; single gaussian curves labeled as QD1 and QD2 associated to two different QD families are also shown (red continuous lines and blue dashed lines, respectively). The arrows indicate the WL (or WL-QW) emission.
Peak energies (full symbols) and FWHM (open symbols) of the QD1 and QD2 PL gaussian components as a function of temperature in InAs QDs capped with In0.2Ga0.8As UCL. The Varshni shift of the InAs energy gap (dashed lines) is included for comparison.
Ensemble and μPL characterization of samples with x = 0.3 and x = 0.1. Red and blue arrows indicate QD1 and QD2 peak energies, respectively.
PL decay curves (dot symbols) at 13 K for QD1 and QD2 families in the x = 0.30 sample. The red straight line corresponds to a monoexponential fit by taking into account the temporal response of the system, as obtained by measuring the laser pulses through the experimental setup (grey-shaded transients).
Arrhenius plots of the integrated PL (a) and the recombination time (b) of the fundamental state QD1 in the four samples. Symbols correspond to the experimental data and straight lines to the simulation.
Arrhenius plots of the integrated PL (a) and the recombination time (b) of the fundamental state QD2 in the four samples. Symbols correspond to the experimental data and straight lines to the simulation.
State diagram proposed to interpret the observed exciton recombination dynamics. Different processes involving the capture, excitation and recombination of carriers in the WL, DS, and GS of QD are indicated by red arrows.
QD1 fitting parameters.
QD2 fitting parameters.
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