Facilely Fabricated Zero-Bias Silicon-Based Plasmonic Photodetector in the Near-Infrared Region with a Schottky Barrier Properly Controlled by Nanoalloys.

Plasmonic Schottky devices have attracted considerable attention for use in practical applications based on photoelectric conversion, because they enable light to be harvested below the bandgap of semiconductors. In particular, silicon-based (Si) plasmonic Schottky devices have great potential for useful photodetection in the near-infrared region. However, the internal quantum efficiency (IQE) values of previously reported devices are low because the Schottky barrier is excessively high. Here, we are the first to develop AuAg nanoalloy-n-type Si plasmonic Schottky devices by cathodic arc plasma deposition. Interestingly, it is found that a novel nanostructure, which leads to the improvement of responsivities, is formed. Moreover, these plasmonic nanostructures can be fabricated in only ∼1 min. The fabricated AuAg nanoparticle-film structure enables proper control of the Schottky barrier height and increases the area of the Schottky interface for electron transfer. As a result, the considerably enhanced IQE of our device at a telecommunication wavelength of 1310 nm (1550 nm) without external bias is 4.6 (6.5) times higher than those in previous reports, and these responsivities are a record high. This approach can be applied to realize efficient photodetection in the NIR region and extend the use of light below the bandgap of semiconductors. This paves the way for future application advancements in a variety of fields, including photodetection, imaging, photovoltaics, and photochemistry.

High-Brightness Red-Emitting Phosphor La3(Si,Al)6(O,N)11:Ce3+ for Next-Generation Solid-State Light Sources.

A novel high-brightness red-emitting phosphor, La3(Si,Al)6(O,N)11:Ce3+ (LSA), which can potentially be used as a laser-excited light source, is demonstrated. Laser-excited phosphor system has great potential for use as a white-light source, as it is orders of magnitude brighter than white LEDs. Although conventional yellow-green phosphors show excellent luminescent properties even under high-power laser excitation, red-emitting phosphors, which are essential to achieve a high color-rendering index and low color-temperature, show quantum efficiency quenching. This limits the output power in multiphosphor excitation systems. Ce3+ should successfully tolerate high-power excitation due to the shortest emission lifetime seen in rare-earth ions, caused by the 5d1-4f1 spin-allowed transition; however, a red-emitting Ce3+-doped phosphor of practical use has not been realized. LSA is described by the crystal-field modification of a yellow-emitting phosphor, La3Si6N11:Ce3+, with substitution of Al in Si sites. LSA shows 640 nm red emission together with tolerance for high-power excitation and thermal quenching, suggesting its significant potential for industrial applications that require ultrahigh brightness.

Resonantly Enhanced Emission from a Luminescent Nanostructured Waveguide.

Controlling the characteristics of photon emission represents a significant challenge for both fundamental science and device technologies. Research on microcavities, photonic crystals, and plasmonic nanocavities has focused on controlling spontaneous emission by way of designing a resonant structure around the emitter to modify the local density of photonic states. In this work, we demonstrate resonantly enhanced emission using luminescent nanostructured waveguide resonance (LUNAR). Our concept is based on coupling between emitters in the luminescent waveguide and a resonant waveguide mode that interacts with a periodic nanostructure and hence outcouples via diffraction. We show that the enhancement of resonance emission can be controlled by tuning the design parameters. We also demonstrate that the enhanced emission is attributable to the accelerated spontaneous emission rate that increases the probability of photon emission in the resonant mode, accompanied by enhanced the local density of photonic states. This study demonstrates that nanostructured luminescent materials can be designed to exhibit functional and enhanced emission. We anticipate that our concept will be used to improve the performance of a variety of photonic and optical applications ranging from bio/chemical sensors to lighting, displays and projectors.

Critical temperature and condensate fraction of a fermion pair condensate.

We report on measurements of the critical temperature and the temperature dependence of the condensate fraction for a fermion pair condensate of 6Li atoms. Bragg spectroscopy is employed to determine the critical temperature and the condensate fraction after a fast magnetic field ramp to the molecular side of the Feshbach resonance. Our measurements reveal evidence of level off of the critical temperature and limiting behavior of condensate fraction near the unitarity limit.

Collisional properties of p-wave Feshbach molecules.

We have observed p-wave Feshbach molecules for all three combinations of the two lowest hyperfine spin states of 6Li. By creating a pure molecular sample in an optical trap, we measured the inelastic collision rates of p-wave molecules. We have also measured the elastic collision rate from the thermalization rate of a breathing mode which was excited spontaneously upon molecular formation.