Search

The coupling behaviors of a radiating dipole with localized surface plasmon (LSP) resonance modes induced on an Ag protrusion in a GaN layer are numerically studied with an algorithm including the feedback effect of LSP resonance to modify the emission behavior of the radiating dipole. Two spectral ranges (400-570 and 570-800 nm) of radiated power enhancement can be observed. The radiated power enhancement in the long-wavelength (short-wavelength) range is generated through the coupling of the radiating dipole with the dipole and quadrupole (higher-order) LSP resonance modes induced on the protrusion. Because the LSP electromagnetic fields of those higher-order modes are mainly distributed around the tip of the protrusion, which is close to the radiating dipole, the radiated power enhancement is quite effective in the blue-green range even though the corresponding metal absorption can be higher than that of a lower-order LSP mode. Compared with the configurations of surface metal nanoparticle (NP) and embedded metal NP, the protrusion structure has the advantages of relatively higher radiated power enhancement in the blue-green spectral range and relatively lower fabrication cost from a practical application viewpoint. [ABSTRACT FROM AUTHOR]

Although a metal grating structure is usually fabricated for momentum-matching a surface plasmon polariton (SPP) with photon, for surface plasmon (SP) coupling application in a light-emitting diode (LED), localized surface plasmon (LSP) on such a structure also plays an important role. We numerically study the LSP resonance behaviors, including the localized resonance behavior of counter-propagating SPP interference, of an Ag grating on GaN. It is found that the resonance behaviors of LSP are controlled not only by the geometry of a grating ridge, but also by grating period, particularly when the grating period is small. In a grating with sharp ridge, large ridge height or width, LSP features of dense charge distributions around the boundaries between ridges and connecting valleys exist. The spectral positions of such LSP features are weakly dependent on the ridge width. Among such features, those with their mode field oscillations across a ridge and hence distributions in an extended space around the ridge can more strongly couple with the quantum wells of an LED. Because of the short coverage range of SPP evanescent field, the localized resonance feature caused by counter-propagating SPP interference has a shorter coupling range. For LED application, an LSP mode with field oscillation across a ridge is preferred. [ABSTRACT FROM AUTHOR]

The enhanced surface plasmon (SP) coupling effects in a blue light-emitting diode (LED) with regularly patterned (REG) surface Ag nanoparticles (NPs) on a dielectric interlayer (DI) of a lower refractive index overgrown on p-GaN are demonstrated. Without a DI, the surface Ag NPs-induced SP coupling with the quantum wells (QWs) in the LED can lead to the increases of internal quantum efficiency and LED output intensity, the reduction of the external quantum efficiency droop effect, and the enhancement of modulation response. By adding a DI, the SP coupling effect is enhanced, resulting in the further improvements of all the aforementioned factors. We compare the SP coupling effects in the LEDs with REG Ag NPs on DIs to those of randomly distributed (RAN) Ag NPs previously reported. Although the variation trends of the localized surface plasmon (LSP) resonance peaks and hence the SP coupling behaviors of REG and RAN Ag NPs are similar, their LSP resonance strengths at the QW emission wavelength are different due to their different spectral patterns of LSP resonance. In other words, although the REG Ag NPs can produce stronger collective LSP resonance with a narrower spectral width, the SP coupling effect depends mainly on the LSP resonance strength at the QW emission wavelength. [ABSTRACT FROM AUTHOR]

The enhancement of the internal quantum efficiency (IQE) of deep-ultraviolet AlxGa1-xN/AlyGa1-yN (x < y) quantum wells (QWs) by fabricating one-dimensional Al nanogratings on a QW structure for inducing surface plasmon (SP) coupling is demonstrated. Through temperature-dependent photoluminescence (PL) measurement, the enhancements of IQE in different emission polarizations are illustrated. Due to the small difference in energy band level between the heavy/light hole and split-off valence bands, the IQEs of the transverse electric- (TE-) and transverse magnetic- (TM-) polarized emissions are about the same. When emission polarization is perpendicular to Al-grating ridges, the SP resonance mode for coupling with the QWs is dominated by localized surface plasmon (LSP). When emission polarization is parallel with Al-grating ridges, the coupled SP resonance mode may mix LSP and SP polariton. In this polarization, LSP can be excited because of the width fluctuation of a grating ridge. When the excitation laser polarization is perpendicular to Al-grating ridges, the strong LSP resonance at the excitation laser wavelength leads to stronger excitation and hence higher IQE levels. [ABSTRACT FROM AUTHOR]

Surface plasmon (SP) coupling behaviors of an InGaN/GaN quantum well (QW) with surface plasmon polariton (SPP) induced on a smooth Ag-film/GaN interface and localized surface plasmon (LSP) induced on randomly distributed surface Ag nanoparticles (NPs) are compared based on temperature-dependent, excitation power-dependent, and time-resolved photoluminescence (PL) measurements. By comparing the variations of PL excitation power-dependent emission at 10 and 300 K, the contribution of SP coupling to the increase of PL intensity can be differentiated from that of PL excitation-intensity increase at the QW due to the enhanced reflection at the Ag/GaN interface. The observed stronger SP coupling effect through SPP, when compared with that through LSP, is attributed to its larger available SP state number per unit area for coupling with the QW. Although the SP coupling strength through LSP on the surface Ag NPs is weakly dependent on PL excitation power, that through SPP at the smooth Ag-film/GaN interface increases significantly with PL excitation power. Such different behavior is due to the abundant SPP states available for coupling with the QW of a higher carrier density. It can also be attributed to the spectral blueshift of QW emission through the screening of the quantum-confined Stark effect and the band filling effect for QW coupling with SPP of a higher density of state. [ABSTRACT FROM AUTHOR]