As the brightness of GaN-based light-emitting diodes (LEDs) has increased, they have recently attracted considerable interest for use in full-color display panels, traffic signals, and solid-state lighting, because of their many advantages, such as long lifetime, small size, and low energy consumption. [1,2] In spite of these advantages, the overall external quantum efficiency, which depends on the internal quantum efficiency (IQE) and the light extraction efficiency (LEE), is still low in conventional In x Ga 1-x N/GaN quantum well (QW) structures. The IQE is strongly influenced by nonradiative recombination processes, by dislocations and other defects, and by separation of the electron and hole wave functions by spontaneous polarization and strain-induced piezoelectric polarization. The LEE is limited by the total internal reflection of generated light and successive re-absorption due to the high refractive index difference between LED structures and air. Recently, it has been suggested that surface plasmons (SPs), excited on a rough metallic surface by the interaction between light and metal, can significantly enhance light emission by improving the IQE. [3][4][5][6][7][8][9][10][11][12][13][14] Although it has been shown that SPs can significantly enhance the quantum efficiency of InGaN emitters, the realization of a GaN-based LED structure with QW-SP coupling has not yet been reported. Here, we demonstrate for the first time an SP-enhanced InGaN/GaN multiple quantum well (MQW) blue LED with a Ag nanoparticle layer inserted between the n-GaN layer and the MQW layer. SPs have attracted great interest because optical properties can be greatly enhanced by coupling between SPs and the QW in LEDs. The coupling of spontaneous emission from the QW into the SP mode can be observed due to the increased absorption at the SP frequency.[10] Time-resolved photoluminescence (TR-PL) measurements showed that the recombination rate in the QW was 90 times faster than spontaneous emission from the QW, when the emission was resonantly coupled to a SP. [11] Recently, Okamoto et al. [12] reported a 14-fold PL enhancement and a 6.8-fold IQE enhancement of InGaN QWs by QW-Ag coupling. Despite the significant enhancement of the IQE of InGaN emitters by SPs, the realization of a GaN-based LED structure with QW-SP coupling is yet to be reported. In previous optical studies [10][11][12] a metal layer was deposited on the surface of the InGaN QW structure together with a GaN spacer layer of thickness 10$12 nm for efficient QW-SP coupling, in order to observe the PL enhancement of the QW, because electron-hole pairs located within the near-field of the QW surface can couple to the SP mode. To realize SP-enhanced LEDs, the metal layer should be deposited on a p-type GaN/MQW structure and the thickness of that p-type GaN layer is critical for QW-SP coupling. The penetration depth of the SP fringing field into the semiconductor is given by Z ¼ l=2p½ð"where " 0 GaN and " 0 metal make up the real part of the dielectric constant of the semicond...

We developed a very effective hyperthermia system for successful photothermal cancer therapy. Instead of applying individual gold nanorods (GNRs) that can absorb NIR light, GNRs were loaded into functional nanocarriers that could provide stable storage of GNRs and selective delivery to a target tumor site. The functional nanocarriers (chitosan-conjugated, Pluronic-based nanocarriers) were prepared by chemically cross-linking Pluronic F 68 with chitosan conjugation to form a flexible, soft, and excellent reservoir for biomacromolecules as well as tumor targeting. In vivo characteristics of the nanocarriers including a long circulation time, a good tumor accumulation, and low liver uptake were previously characterized by us. When GNRs were delivered by using these nanocarriers, much enhanced in vitro cellular uptake and a photothermal effect were observed for a cancer cell line. More importantly, an intravenous injection of this system followed by NIR laser irradiation to the tumor site resulted in a very efficient thermolysis in vivo. Thus, apparently complete tumor resorption was achieved without damage to the surrounding tissue, suggesting a promising candidate for clinical phototherapeutic applications.

Effective light emission from low-dimensional silicon materials such as porous silicon, silicon nanocrystals, and superlattices has been demonstrated at room temperature in spite of the indirect bandgap nature of bulk silicon. [1][2][3][4][5] In particular, silicon quantum dot (Si QD) light-emitting diodes (LEDs) have recently been investigated as a promising light source for the next generation of optical interconnections. [6][7][8] However, the quest for highly efficient Si QD LEDs remains unfulfilled. To achieve this goal, new LED structures are being developed to enhance the external quantum efficiency (h ext ), which is a product of the light-extraction efficiency (h extraction ), radiative efficiency (h rad ), and current-injection efficiency (h inj ). [9] Among the new approaches, increasing the radiative recombination rate by coupling QDs to surface plasmons (SPs, collective charge oscillations at the interface between a metal and a dielectric material) has attracted a great deal of attention. [10][11][12] Although enhanced photoluminescence (PL)of SP-coupled nanostructures such as QDs [13][14][15][16][17] and quantum wells (QWs) [18] has been reported, there has been no report concerning the enhancement of electroluminescence (EL) in Si QD LEDs through a Si QD-SP coupling effect. Here, we show the first evidence of enhanced h ext in a Si QD LED resulting from the coupling between Si QDs and localized surface plasmons (LSPs) and effective current tunneling into Si QDs from an Ag layer containing Ag particles inserted between the Si QD layer and Si substrate. Surface plasmon excitations in bounded geometries, such as nanostructured metallic particles, are LSPs. The resonant excitation of LSPs on the surface of nanostructured metallic particles by an incident electromagnetic field (light) causes strong light scattering and absorption, and enhanced local electromagnetic fields. LSPs are generally used in many applications such as ultrafast switches, optical tweezers, labeling biomolecules, optical filters, biosensors, surface-enhanced spectroscopies, plasmonics, and chemical sensors. [19][20][21][22] SPs are evanescent waves that exponentially decay with distance from a metal surface. Si QDs located within the near-field of the metal surface can be effectively coupled to SP mode. [13,18,19] In order to keep the close distance between SiQDs and the metal layer for Si QD-LSP coupling, we propose a Si QD LED structure with an Ag layer containing Ag particles inserted between the silicon nitride layer containing Si QDs and the Si substrate layer, as shown in Figure 1. Figure 2a and b shows cross-sectional transmission electron microscopy (TEM) images of Si QD LEDs with and without an Ag layer. Figure 2a depicts the interface between the silicon nitride and Si substrate of a reference Si QD LED. Figure 2b is an image of the interfaces between the silicon nitride layer, Ag layer, and the Si substrate. The silicon nitride film deposited on the Ag layer was similar in thickness to the silicon nitride layer in the re...

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The GaAs quantum dots (QDs) on an AlGaAs∕GaAs (111)A surface grown by a droplet epitaxy have a density of 1.6×1011∕cm2, which is relatively higher than those (1.3×1010∕cm2) on an AlGaAs∕GaAs (001) surface. The formation of highly dense GaAs QDs on the (111)A surface can be explained by the relatively short surface migration of Ga atoms. The GaAs QDs on AlGaAs∕GaAs (111)A showed the intense photoluminescence (PL) and a relatively narrower PL linewidth compared to that of the GaAs QDs on AlGaAs∕GaAs (001), indicating that the QDs on the GaAs (111)A substrate have a high crystal quality and high uniformity than those on GaAs (001).