One-dimensional miniband formation in closely stacked InAs/GaAs quantum dots

We have studied the electronic states of closely stacked InAs/GaAs quantum dots (QDs) with a 4.0-nm spacer layer using linearly polarized photoluminescence (PL) and time-resolved PL measurements. An increase in the stacking-layer number (SLN) leads to an increase in the linear polarization anisotropy in the (001) plane; the [$-$110]-polarization component becomes dominant. These SLN-dependent polarization characteristics result from the valence-band mixing induced by the vertically coupled electronic states. The PL spectrum of the stacked QDs shows clear blueshifts with an increase in the excitation power because of the band filling. In addition, the radiative recombination lifetime has been found to obey the $T^{1/2}$ dependence, which directly confirms the one-dimensional translational motion of excitons in the closely stacked QDs.

Figure 1

(a) ($-$110) and (b) (110) cross-sectional TEM images of the 20 stacked InAs QDs.

Figure 2

Linearly polarized PL spectra from the (a) ($-$110)-cleaved surface and (b) (001) surface.

Figure 3

(a) Unpolarized and (b) polarized PL spectra from the (001) surface at 16 K.

Figure 4

PL spectra excited by 659-nm (dashed line) and 532-nm (solid line) wavelength laser diodes.

Figure 5

Excitation power dependence of the PL spectra of the (a) single-layer, (b) 9, (c) 15, (d) 20, and (e) 30 stacked InAs QDs at 16 K.

Figure 6

(a) SLN dependence of the PL decay profile at 3.1 K, which was detected at ${\lambda }_0$±1 nm. (b) SLN dependence of the PL decay lifetime. The dashed line shows the exciton Bohr diameter in bulk InAs.

Figure 7

Temperature dependence of the PL decay profiles of the (a) single-layer, (b) 9, (c) 15, (d) 20, and (e) 30 stacked InAs QDs, which were detected at ${\lambda }_0$±1 nm. (f)–(j) Temperature dependence of the PL decay lifetime in each the sample. The solid line indicates the $T^{1/2}$ dependence.