The high performance of a light-emitting diode (LED) with the total p-type thickness as small as 38 nm is demonstrated. By increasing the Mg doping concentration in the p-AlGaN electron blocking layer through an Mg pre-flow process, the hole injection efficiency can be significantly enhanced. Based on this technique, the high LED performance can be maintained when the p-type layer thickness is significantly reduced. Then, the surface plasmon coupling effects, including the enhancement of internal quantum efficiency, increase in output intensity, reduction of efficiency droop, and increase of modulation bandwidth, among the thin p-type LED samples of different p-type thicknesses that are compared. These advantageous effects are stronger as the p-type layer becomes thinner. However, the dependencies of these effects on p-type layer thickness are different. With a circular mesa size of 10 μm in radius, through surface plasmon coupling, we achieve the record-high modulation bandwidth of 625.6 MHz among c-plane GaN-based LEDs.
The efficiency enhancement of light color conversion from blue quantum well (QW) emission into red quantum dot (QD) emission through surface plasmon (SP) coupling by coating CdSe/ZnS QDs on the top of an InGaN/GaN QW light-emitting diode (LED) is demonstrated. Ag nanoparticles (NPs) are fabricated within a transparent conductive Ga-doped ZnO interlayer to induce localized surface plasmon (LSP) resonance for simultaneously coupling with the QWs and QDs. Such a coupling process generates three enhancement effects, including QW emission, QD absorption at the QW emission wavelength, and QD emission, leading to an overall enhancement effect of QD emission intensity. An Ag NP geometry for inducing an LSP resonance peak around the middle between the QW and QD emission wavelengths results in the optimized condition for maximizing QD emission enhancement. Internal quantum efficiency and photoluminescence (PL) decay time measurements are performed to show consistent results with LED performance characterizations, even though the QD absorption of PL excitation laser may mix with the SP-induced QD absorption enhancement effect in PL measurement.
We first illustrate the faster decrease of the photothermal (PT) effect with the delay time of laser treatment, in which the illumination of a 1064 nm laser effectively excites the localized surface plasmon (LSP) resonance of cell-up-taken gold nanoring (NRI) linked with a photosensitizer (PS), when compared with the photodynamic (PD) effect produced by the illumination of a 660 nm laser for effective PS excitation. The measurement results of the metal contents of Au NRI and PS based on inductively coupled plasma mass spectroscopy and the PS fluorescence intensity based on flow cytometry show that the linkage of NRI and PS is rapidly broken for releasing PS through the effect of glutathione in lysosome after cell uptake. Meanwhile, NRI escapes from a cell with a high rate such that the PT effect decays fast while the released PS can stay inside a cell longer for producing a prolonged PD effect. The effective delivery of PS through the linkage with Au NRI for cell uptake and the advantageous effect of LSP resonance at a PS absorption wavelength on the PD process are also demonstrated.
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