More than a century after the introduction of incandescent lighting and half a century after the introduction of fluorescent lighting, solid-state light sources are revolutionizing an increasing number of applications. Whereas the efficiency of conventional incandescent and fluorescent lights is limited by fundamental factors that cannot be overcome, the efficiency of solid-state sources is limited only by human creativity and imagination. The high efficiency of solid-state sources already provides energy savings and environmental benefits in a number of applications. However, solid-state sources also offer controllability of their spectral power distribution, spatial distribution, color temperature, temporal modulation, and polarization properties. Such "smart" light sources can adjust to specific environments and requirements, a property that could result in tremendous benefits in lighting, automobiles, transportation, communication, imaging, agriculture, and medicine.

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Diode ideality factors much higher than the expected values of 1.0 to 2.0 have been reported in GaN-based p-n junctions. It is shown that moderately doped unipolar heterojunctions as well as metal-semiconductor junctions, in particular the metal contact to p-type GaN, can increase the ideality factor to values greater than 2.0. A relation is derived for the effective ideality factor by taking into account all junctions of the diode structure. Diodes fabricated from a bulk GaN p-n junction and a p-n junction structure with a p-type AlGaN/GaN superlattice display ideality factors of 6.9 and 4.0, respectively. These results are consistent with the theoretical model and the fact that p-type AlGaN/GaN superlattices facilitate the formation of low-resistance ohmic contacts.

GaInN LEDs with a six‐layer graded‐ refractive‐index antireflection coating made entirely of indium tin oxide (ITO) are demonstrated to have 24.3 % higher light output than LEDs with dense ITO coating. The increased light‐output of the LEDs with graded‐refractive‐index antireflection coating is attributed to the virtual elimination of Fresnel reflection and surface roughening of low‐refractive index ITO.

Zinc-embedded silica nanoparticle layer in a multilayer coating on a glass substrate achieves broadband antireflection and high transparency Application of plasma enhanced chemical vapor deposition silicon nitride as a double layer antireflection coating and passivation layer for polysilicon solar cells Design, fabrication, and characterization of a broadband, omnidirectional, graded-index antireflection ͑AR͒ coating made using nanostructured low-refractive-index ͑n = 1.05-1.40͒ silica deposited by oblique-angle deposition are reported. Averaged over wavelength range from 400 to 1100 nm and 0°-90°angle of incidence, polished Si reflects ϳ37% of incident radiation. The reflection losses are reduced to only 5.9% by applying a three-layer graded-index AR coating to Si. Our experimental results are in excellent agreement with theoretical calculations. The AR coatings reported here can be optimized for photovoltaic cells made of any type of material.