Magnetically controlled exciton transfer in hybrid quantum-dot–quantum-well nanostructures

A magnetophotoluminescence study of the carrier transfer with hybrid InAs/GaAs-quantum-dot–InGaAs-quantum-well structures is carried out where we observe an unusual dependence of the photoluminescence (PL) on the GaAs barrier thickness at strong magnetic field and excitation density. For the case of a thin barrier the quantum-well (QW) PL intensity is observed to increase at the expense of a decrease in the quantum-dot (QD) PL intensity. This is attributed to changes in the interplane carrier dynamics in the QW and the wetting layer (WL) resulting from increasing the magnetic field along with changes in the coupling between QD excited states and exciton states in the QW and the WL.

Figure 1

PL spectra measured for (a) reference InAs QD and (b) reference ${\mathrm{In}}_{0.13}{\mathrm{Ga}}_{0.87}\mathrm{As}$ QW. The inset shows the LL splitting (solid lines are guides to the eye). Hybrid dot-well structures are shown with $d_{sp}=20\mathrm{nm}$ for (c) QD and (d) QW and with $d_{sp}=2\mathrm{nm}$ for (e) QD and (f) QW under high excitation power $P_{\text{ex}}=90\mu \mathrm{W}$. For all datasets are represented the detected polarizations ${\sigma }^{+}$(black lines) and ${\sigma }^{-}$(red lines) at 9 T and the spectra without magnetic field (blue lines). Gaussian fittings for the ground-state QD and first excited QD states are shown in Fig. 1.

Figure 2

(a) Integrated PL intensities for QD (left axes) and QW (right axes) ground state vs magnetic field measured in (a) reference QD and QW, (b) QD-QW hybrid dot-well structure separation $d_{sp}=20\mathrm{nm}$, and (c) QD-QW hybrid dot-well structure with $d_{sp}=2\mathrm{nm}$ at $P_{\text{ex}}=90\mathrm{W}$. Filled and hollow spheres represent the circular ${\sigma }^{+}$ and ${\sigma }^{-}$ polarized luminescence detection, respectively.

Figure 3

(a) Diamagnetic shift vs magnetic field measured for the QW emission in the hybrid structures with $d_{sp}=2$ and 20 nm and in the reference QW at $P_{\text{ex}}=90\mu \mathrm{W}$. (b) Comparison between WKB approximation and experimental QW integrated PL intensity.