7,824 research outputs found
Thin-film photonic crystal LEDs with enhanced directionality
No full textThe use of photonic crystals for light extraction from light-emitting diodes (LEDs)
gives the possibility to shape the farfield emission pattern. This is of particular interest
for étendue-limited LED applications that require a more directional farfield than state-
of-the-art Lambertian emitters. However, the application of a photonic crystal in a LED
results in directional emission only if the photonic crystal and the distribution of guided
modes in the LED are tuned correctly. In this thesis, red- and blue-emitting thin-film
PhC-LEDs in the AlGaInP and InGaN material systems were modelled, designed,
fabricated and characterized. The first experimental results show that light extraction
with photonic crystals from AlGaInP thin-film LEDs several microns thick is neither
directional nor more efficient than state-of-the-art LEDs with a rough surface structure.
Directional light extraction for AlGaInP PhC-LEDs is for the first time demonstrated in
much thinner devices where the photonic crystal light extraction of guided modes is
combined with the resonant-cavity effect. In an attempt to approach the ideal PhC-LED,
strong photonic crystal farfield shaping is demonstrated in InGaN thin-film LEDs of
sub-micron thickness. Analysis of their spectral farfields unexpectedly shows that high
order diffraction contributes significantly to the light extraction efficiency if the mode
absorption is sufficiently low. It is also demonstrated that directional photonic crystal
light extraction is possible in InGaN thin-film LEDs several microns thick. The
directionality stems from the modulation of the spontaneous emission caused by the
proximity of the active region to the bottom mirror. Two new concepts for enhanced
light extraction and high directionality are presented: Photonic crystals with two
dominating lattice constants are found to outperform conventional photonic crystal
LEDs. An alternative approach is the dielectric PhC-LED - FDTD simulations show
that the high extraction efficiency of LEDs with surface roughness is combined with the
higher directionality of photonic crystal light extraction
Harriet Kelly
No full textHarriet Kelly, wife of Charles Kelly, is shown here with Josiah Gibbs and Frank Beckwith at Marysvale, Utah. Charles Kelly was a printer, artist, author, historian, the first superintendent of Capitol Reef National Park
Charles Kelly
No full textCharles Kelly is shown in this image at age 82. Charles Kelly was a printer, artist, author, historian, the first superintendent of Capitol Reef National Park
IC<sub>50</sub> values from the crystal violet assay in Kelly cells.
No full text<p>IC<sub>50</sub> values from the crystal violet assay in Kelly cells.</p
Charles Kelly
No full textCharles Kelly was a printer, artist, author, historian, the first superintendent of Capitol Reef National Park
Charles Kelly
No full textCharles Kelly was a printer, artist, author, historian, the first superintendent of Capitol Reef National Park
Charles Kelly
No full textCharles Kelly was a printer, artist, author, historian, the first superintendent of Capitol Reef National Park
Charles Kelly
No full textCharles Kelly was a printer, artist, author, historian, the first superintendent of Capitol Reef National Park
Charles Kelly
No full textCharles Kelly was a printer, artist, author, historian, the first superintendent of Capitol Reef National Park
Charles Kelly
No full textCharles Kelly, with his wife Harriet, was a printer, artist, author, historian, the first superintendent of Capitol Reef National Park
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