Localized surface plasmon resonances can increase the quantum efficiency of photon emitters through both absorption and spontaneous emission enhancement effects. Despite extensive studies, experimental results that clearly distinguish the two plasmonic enhancement effects are rarely available. Here, we present clear spectral signatures of the plasmonic enhancement effects on the absorption (excitation) and spontaneous emission (Purcell factor) by analyzing the temperature dependent photoluminescence (PL) properties of InGaAs/GaAs single quantum well (QW) coupled to colloidal gold nanorods (AuNRs) at different GaAs capping layer thickness (d). We find that when the emitting InGaAs layer is close to the AuNRs (d = 5 nm), the plasmonic enhancement effect on the QW PL is dominated by the Purcell factor that significantly increases the external quantum efficiency of the QW that otherwise barely emits. When d is increased to 10 nm, the temperature dependence of the PL enhancement factor (F) reflects absorption enhancement in the capping layer followed by carrier diffusion and capture by the well. First F increases with temperature and then decreases following the temperature dependence of the carrier diffusion coefficient in GaAs. By factoring out the contribution of the captured carriers to F, it is shown that carrier transfer to the well reaches saturation with increasing incident laser power. In addition to providing insight into the plasmonic enhancement mechanism, the results presented in this work suggest that colloidal plasmonic nanoparticles can be used as simple probes for understanding carrier transport phenomena in arbitrary semiconductor heterostructures.
Compared to the highly sensitive silicon based affordable visible light detectors, infrared photodetectors require significant improvement. Localized surface plasmon resonances of metal nanoparticles can be utilized for increasing the absorption efficiency of semiconductors suited for detection of infrared radiation. In this work, plasmonic gold nanorods (AuNRs) are used to enhance generation of charge carriers and photon emission by InAs/InGaAs/GaAs quantum dots-in-a-well semiconductor heterostructures. Comparison of measured and calculated scattering spectra reveals that the AuNRs on GaAs exhibit red to green colors depending on their proximity to the GaAs surface. On the other hand, theoretical and experimental near-field optical characterization show that the electric field is tightly localized at the AuNR-GaAs interfacial regions, creating a convenient platform for investigating localized carrier generation and diffusion by monitoring the emission of InAs QDs. The carrier generation and photon emission enhancement is studied as a function of the GaAs thickness (distance) and temperature. Analysis of the QD emission enhancement as a function of distance reveals a Förster radius of 3.85 ± 0.15 nm, a near-field decay length of 4.8 ± 0.1 nm and an effective carrier diffusion length of 64.0 ± 3.0 nm. These distance parameters indicate two emission enhancement mechanisms: plasmon enhanced carrier generation inside the GaAs layer and diffusion to the InAs QDs, and direct near-field excitation of the InAs/InGaAs quantum well. The emission enhancement increases with temperature, confirming the importance of charge carrier diffusion from the GaAs to the InAs QDs, where recombination and photon emission takes place.
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