Superlinear Photoluminescence Dynamics in Plasmon–Quantum-Dot Coupling Systems

Light–matter interaction exploiting plasmons is attracting great interest in terms of a new twist, hot electrons. We designed a basic configuration to couple plasmonic metasurfaces with a layer of quantum dots (QDs) embedded in semiconductors and experimentally investigated the photoluminescence (PL) dynamics in the coupled systems of III–V semiconductor QDs with plasmonic metasurfaces. The QDs of InAs, which emit luminescence at telecom wavelengths near 1300 nm, were grown on GaAs substrates with a molecular-beam-epitaxy technique. The plasmonic metasurfaces were fabricated on top of the GaInAs substrates, using a numerical design for single-layer Au metasurfaces. Here we show that the PL responses through the plasmonic metasurface becomes more active in the coupled systems than those in the QDs without the plasmonic metasurfaces, being superlinear with respect to the excitation laser intensity, even under weak continuous-wave excitation. The superlinear responses are successfully described in a general theoretical model, incorporating hot-electron contributions by the plasmonic metasurfaces to the PL processes. We examined the PL responses at room temperature and a low temperature of 9 K and found that the hot electrons mainly contribute to superlinear PL responses at room temperature, whereas induced transitions between the excitonic levels in the QDs are significant at 9 K. Thus, our systematic study enables discrimination of the origins of the nonobvious PL responses. In particular, this study provides a new insight for the active contributions by hot electrons to photoexcited processes at room temperature.