Recent advances in chemical synthesis have made it possible to produce gold and silver nanowires that are free of large-scale crystalline defects and surface roughness. Surface plasmons can propagate along the wires, allowing them to serve as optical waveguides with cross sections much smaller than the optical wavelength. Gold nanowires provide improved chemical stability as compared to silver nanowires, but at the cost of higher losses for the propagating plasmons. In order to characterize this trade-off, we measured the propagation length and group velocity of plasmons in both gold and silver nanowires. Propagation lengths are measured by fluorescence imaging of the plasmonic near fields. Group velocities are deduced from the spacing of fringes in the spectrum of coherent light transmitted by the wires. In contrast to previous work, we interpret these fringes as arising from a far-field interference effect. The measured propagation characteristics agree with numerical simulations, indicating that propagation in these wires is dominated by the material properties of the metals, with additional losses due to scattering from roughness or grain boundaries providing at most a minor contribution. The propagation lengths and group velocities can also be described by a simple analytical model that considers only the lowest-order waveguide mode in a solid metal cylinder, showing that this single mode dominates in real nanowires. Comparison between experiments and theory indicates that widely used tabulated values for dielectric functions provide a good description of plasmons in gold nanowires but significantly overestimate plasmon losses in silver nanowires.

Phosphor-containing white light-emitting diodes (LEDs) with low color-correlated temperatures (CCTs) and high color rendering indexes (CRIs) are highly desirable for energy-efficient and environmentally friendly solid-state light sources. Here, we report a new and efficient blue light-excited, green-emitting Ce3+-activated CaY2ZrScAl3O12 phosphor, which underpins the fabrication of high-color quality and full-visible-spectrum warm-white LED devices with ultrahigh CRI values (Ra > 96 and R9 > 96). A family of CaY2ZrScAl3O12:Ce3+ phosphors with different Ce3+ dopant concentrations were prepared by high-temperature solid-state synthesis. X-ray diffraction and corresponding Rietveld refinement reveal a garnet structure with an Ia3̅d space group and crystallographic parameters a = b = c = 12.39645(8) Å, α = β = γ = 90°, and V = 1904.99(4) Å3. Luminescence properties were studied in detail as a function of Ce3+ with the optimal concentration 1% mol. Impressively, CaY2ZrScAl3O12:1%Ce3+ exhibits a broad excitation band from 370 to 500 nm, peaking at ∼421 nm, which is well matched with emission from commercial blue LED chips. Under 421 nm excitation, the CaY2ZrScAl3O12:1%Ce3+ phosphor produces dazzling green light in a wide emission band from 435 to 750 nm (emission peak: 514 nm; full width at half-maximum: 113 nm), with a high internal quantum efficiency of 63.1% and good resistance to thermal quenching (activation energy of 0.28 eV). A white LED device combining a 450 nm blue LED chip with CaY2ZrScAl3O12:1%Ce3+ green phosphor and commercial CaAlSiN3:Eu2+ red phosphor as color converters demonstrates bright warm-white light with excellent CIE color coordinates of (0.3938, 0.3819), low CCT of 3696 K, high CRI (Ra = 96.9, R9 = 98.2), and high luminous efficacy of 45.04 lm W–1 under a 20 mA driving current. New green phosphors enable the design and implementation of efficient luminescent materials for healthy solid-state lighting.

An approach to realizing high-voltage, high-current vertical GaN-on-GaN power diodes is reported. We show that by combining a partially compensated ion-implanted edge termination (ET) with sputtered SiNx passivation and optimized ohmic contacts, devices approaching the fundamental material limits of GaN can be achieved. Devices with breakdown voltages (Vbr) of 1.68 kV and differential specific on resistances (Ron) of 0.15 mΩ cm2, corresponding to a Baliga figure of merit of 18.8 GW/cm2, are demonstrated experimentally. The ion-implantation-based ET has been analyzed through numerical simulation and validated by experiment. The use of a partially compensated ET layer, with approximately 40 nm of the p-type anode layer remaining uncompensated by the implant, is found to be optimal for maximizing Vbr. The implant-based ET enhances the breakdown voltage without compromising the forward characteristics. Devices exhibit near-ideal scaling with area, enabling currents as high as 12 A for a 1 mm diameter device.

Epitaxial p-i-n structures grown on native GaN substrates have been fabricated and used to extract the impact ionization coefficients in GaN. The photomultiplication method has been used to experimentally determine the impact ionization coefficients; avalanche dominated breakdown is confirmed by variable-temperature breakdown measurements. To facilitate photomultiplication measurements of both electrons and holes, the structures include a thin pseudomorphic In0.07Ga0.93N layer on the cathode side of the drift layer. Illumination with 193 nm and 390 nm UV light has been performed on diodes with different intrinsic layer thicknesses. From the measured multiplication characteristics, the impact ionization coefficients of electrons (α) and holes (β) were determined for GaN over the electric field range from 2 MV/cm to 3.7 MV/cm. The results show that for transport along the c-axis, holes dominate the impact ionization process at lower electric field strengths; the impact ionization coefficient of electrons becomes comparable to that of holes (β/α<5) for electric field strengths above 3.3 MV/cm.