When an atomic impurity is incorporated in a nanoparticle of size 2 to 10 nm, the quantum-confinement provided by the dielectric-boundary of the host-nanoparticle modulates the properties of the atom. This Quantum Confined Atom (QCA) shows extraordinary changes in its luminescent properties and is associated with the modulation of the excited states of the caged atom. These “atomically engineered nanomaterials,” pioneered and developed by Nanocrystals Technology, yield several novel properties and are expected to be a major contributor to the future of nanotechnology. Efficient QCA-Nanophosphors that emit different colors depending on the specific choice of the 'caged atom' are being developed for applications to solid-state lighting. We have made two key contributions to development of SSL. (1) By embedding nanoparticles in the encapsulant, the refractive index is enhanced to 1.8 that allows us to enhance Light Extraction Efficiency (LEE) of the LED chip. (2) Incorporation of appropriate nanophosphors enables efficient down-conversion with high color-quality. The combination of an optically transparent downconverter and high refractive index in an encapsulant has yielded Phosphor-Converted LEDs (PC-LEDs) that yield higher package optical efficiency at lower package-level cost. The LEE and wall plug efficiency enhancement due to the HRI encapsulant is applicable across the entire visible spectrum of monochromatic HB-LED lamps.
The annealing behavior of Hg1CdTe layers, grown by the conventional Organometallic
Vapor Phase Epitaxy (OMVPE) , is reported. As grown layers, which are p-type with a concentration
around 4 x 10'6/cm3 of mercury vacancies, become light p-type with carrier concentrations
around 1-2x 10'5/cm3 after Hg saturated annealings at temperatures in the range of
200-230°C. These conditions, usually sufficient for the complete annealing of bulk Hg1_CdTe,
to n-type, are thus inadequate for OMVPE grown epilayers. The as grown layers are converted
to n-type with a carrier concentration of approximately 5 x 10'4/cm3 by a higher temperature
anneal at 290°C, followed by a low temperature anneal at 220°C.
Hall effect measurements were made under variable temperature as well as variable magnetic
field conditions. Bulk carrier concentrations and mobilities were evaluated by considering
the effect of the surface inversion/accumulation layer on the Hall data. It is proposed that ptype
conduction in the partially annealed layers is due to the persistence of vacancies in the
Hg1_CdTe layer, which are not completely annihilated during the low temperature anneal.
Conversion to n-type is probably due to residual donor impurities in the as grown Hg1_CdTe
layer.
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