Plasmon mediated energy transfer in hybrid quantum well-quantum dot system

Abstract

In this thesis silver plasmonic arrays, fabricated using both helium-ion lithography (HIL) and electron beam lithography (EBL), on an InGaN/GaN quantum well (QW) are used to enable localised surface plasmon (LSP) enhanced Forster resonance energy transfer (FRET) to a ~ 80 nm layer of CdSe/ZnS quantum dots (Qds) embedded in a poly(methyl methacrylate) (PMMA) matrix. The thickness of the QD acceptor layer and the dimensions of the silver plasmonic nanoparticles (Nps) are large compared with previous reports of plasmon-coupled nonradiative energy transfer (FT). Whilst FRET has been observed between a QW and QDs before, the work presented in this thesis provides the first ever experimental demonstration of LSP enhanced FRET from a QW donor to a thick layer of QD acceptors. In particular, the carrier density dependence of the plasmon-coupled nonradiative energy transfer mechanism is investigated, which is a first step towards FRET based implementation in electrically pumped LEDs. By conducting the carrier density dependence the LSP enhanced mechanism within the system is found to be determined by the same physics as conventional FRET. The plasmon-coupled FRET efficiency is determined by the interplay between the QW donor spontaneous emission rate, the rate of nonradiative FT to the plasmonic array and the rate of plasmon-coupled nonradiative FT to the acceptors. TRPL and spectral measurements are used to demonstrate and quantify the LSP-FRET from the QWs to the QDs. Both the QW emission quenching rate and the plasmon-coupled nonradiative FT rate are found to increase with increasing QW carrier density. The quenching and energy transfer efficiencies are carrier density independent. Despite strong direct quenching by the metal nanoparticles, the LSP-FRET results in a plasmon-enhanced energy transfer efficiency of 25 % and a 16 % increase of the QD emission.