Further reduction of the efficiency droop effect and further enhancements of internal quantum efficiency (IQE) and output intensity of a surface plasmon coupled, blue-emitting light-emitting diode (LED) by inserting a dielectric interlayer (DI) of a lower refractive index between p-GaN and surface Ag nanoparticles are demonstrated. The insertion of a DI leads to a blue shift of the localized surface plasmon (LSP) resonance spectrum and increases the LSP coupling strength at the quantum well emitting wavelength in the blue range. With SiO2 as the DI, a thinner DI leads to a stronger LSP coupling effect, when compared with the case of a thicker DI. By using GaZnO, which is a dielectric in the optical range and a good conductor under direct-current operation, as the DI, the LSP coupling results in the highest IQE, highest LED output intensity, and weakest droop effect.
First, the experimental implementations and theoretical/numerical investigations of surface plasmon (SP) coupled InGaN/GaN quantum-well lightemitting diodes (LEDs) are reviewed. If the p-GaN layer in an LED can be thin, surface metal nanoparticle (NP) is an inexpensive structure for inducing effective SP coupling. When the p-GaN layer is thick, a few metal structures, including metal protrusion, buried metal NP, and embedded metal NP, can be used for effective SP coupling. In the numerical study, an algorithm, including the feedback effect of the induced SP resonance on the radiating behavior of the source dipole, has been proposed for studying the SP coupling effects with an embedded metal NP, a surface metal NP, and a metal protrusion. Then, the theoretical formulations and numerical algorithms for evaluating the radiated power enhancement in the coupling process between two radiating dipoles and the localized surface plasmon (LSP) induced on a nearby Ag NP are built. Three mechanisms are considered in the coupling process for radiated power enhancement, including the interference of the two phase-retarded radiation contributions from the two dipoles, the interaction between the two dipoles, and the LSP resonant coupling.
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