(Color online) plan views of the uncapped single layer QD sample (a) and of the upper layer of the double layer QD sample having the spacer of (b). The size and height histograms associated with each image are also shown in (c)–(f).
⟨110⟩ cross-sectional TEM images of the double vertically stacked QDs separated by spacers of (a) and (b). High resolution TEM image of the double layer QDs with the spacer of (c).
PL spectra of double layer QDs with different spacer thicknesses : 10, 8, 6, and . PL signal of the single layer is also reported as reference. Excitation power density is .
Gaussian fits to the PL spectra as a function of the power excitation density of the single (a) and the double layer QDs with the spacer of (b).
(Color online) PL peak positions for the single (a) and the double layer QDs with the spacer of (b). The numbers that label the PL peaks correspond to those of Fig. 4.
Schematic representation of the model used in the calculations to simulate a couple of vertically stacked QDs.
Comparison between experimental (close symbols) and theoretical (lines) transition energies for the single and double layer QDs as a function of the spacer thickness . Experimental transition energies are obtained from multi-Gaussian curve fits of PL spectra recorded with an excitation optical density of . Material parameters and QD characteristics used in the calculations are reported in Tables I and II, respectively. In double layer QDs two transitions are observed for each shell: , , at lower energy associated with (larger) upper layer dots and , , at higher energy associated with (smaller) bottom layer dots. The experimental data obtained for (open symbols) cannot be compared with the reported theoretical lines because of the reduced size of QDs.
Material parameters used in the calculations.
Structural characteristics of QD samples used in the calculations for the comparison with the experimental data.
Article metrics loading...
Full text loading...