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...

Crystalline silicon quantum dots (Si QDs) were spontaneously grown in the silicon nitride films by plasma-enhanced chemical vapor deposition using SiH4 and NH3 as precursors. When the size of the Si QDs was reduced from 4.9 to 2.9nm, the photoluminescence peak energy was shifted from 1.73 to 2.77eV. The photoluminescence peak energy was fitted to the relationship, E(eV)=1.13+13.9∕d2, where d is the diameter of the Si QD in nanometers. The measured band-gap energies of the Si QDs were in good agreement with the quantum confinement model for crystalline Si QDs. These results suggest that the hydrogen dissociated from NH3 plays an important role in improving the crystallinity and surface passivation of Si QDs.

The photoluminescence (PL) property of crystalline silicon quantum dots (Si QDs) in silicon nitride grown by using ammonia and silane gases is reported. The peak position of PL could be controlled in the wavelength range from 450 to 700 nm by adjusting the flow rates of ammonia and silane gases. The PL intensity of Si QDs grown by ammonia was more intense compared to that of Si QDs grown by nitrogen gas. To investigate the role of hydrogen in the PL enhancement, the Si QDs grown by nitrogen gas were postannealed under hydrogen ambient. The enhancement in PL intensity was attributed to the hydrogen passivation of dangling bonds related to silicon and/or nitrogen at the interface of Si QDs and silicon nitride.

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...

The purpose of this study was to present clinical and MR imaging features of intra-articular ganglion cysts of the knee. Retrospective review of 1685 consecutive medical records and MR examinations of the knee performed at three imaging centers allowed identification of 20 patients (13 men and 7 women; mean age 35 years), in whom evidence of intra-articular ganglion cyst was seen. Of the 20 ganglion cysts, 5 were found in the infrapatellar fat pad, 10 arose from the posterior cruciate ligament, and 5 from the anterior cruciate ligament. Three of five patients with ganglion cyst in the infrapatellar fat pad had a palpable mass. In 7 of 15 patients with ganglion cyst in the intercondylar notch, exacerbation of pain occurred in a squatting position. On four MR arthrographies, ganglion cysts were an intra-articular round, lobulated, low signal intensity lesion. Five cases of fat-suppressed contrast-enhanced T1-weighted SE images demonstrated peripheral thin rim enhancement. The clinical presentation of intra-articular ganglion cyst is varied according to its intra-articular location. The MR appearance of intra-articular ganglion cyst is characteristic and usually associated with the cruciate ligament or the infrapatellar fat pad. Magnetic resonance arthrography has no definite advantage over conventional MR in the evaluation of the lesion. For intra-articular ganglion cyst in the infrapatellar fat pad, fat-suppressed contrast-enhanced MR imaging could be useful, because a thin, rim-enhancing feature of intra-articular ganglion cyst allows it to be distinguished from synovial hemangioma and synovial sarcoma.