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Gallium nitride based logpile photonic crystals for visible lighting

Proceedings of SPIE - The International Society for Optical Engineering

Subramania, G.; Li, Q.; Lee, Y.J.; Figiel, J.J.; Sanchez, Carlos A.; Wang, George T.; Fischer, Arthur J.; Biswas, R.

Photonic crystals (PC) can fundamentally alter the emission behavior of light sources by suitably modifying the electromagnetic environment around them. Strong modulation of the photonic density of states especially by full threedimensional (3D) bandgap PCs, enables one to completely suppress emission in undesired wavelengths and directions while enhancing desired emission. This property of 3DPC to control spontaneous emission, opens up new regimes of light-matter interaction in particular, energy efficient and high brightness visible lighting. Therefore a 3DPC composed entirely of gallinum nitride (GaN), a key material used in visible light emitting diodes can dramatically impact solid state lighting. The following work demonstrates an all GaN logpile 3DPC with bandgap in the visible fabricated by a template directed epitaxial growth. © 2012 SPIE.

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TYPE Conference YEAR 2012
ScopusOSTI

Top-down fabrication of GaN-based nanorod LEDs and lasers

Proceedings of SPIE - The International Society for Optical Engineering

Wang, George T.; Li, Qiming L.; Wierer, Jonathan W.; Figiel, J.J.; Wright, Jeremy B.; Luk, Ting S.; Brener, Igal B.

Although planar heterostructures dominate current optoelectronic architectures, 1D nanowires and nanorods have distinct and advantageous properties that may enable higher efficiency, longer wavelength, and cheaper devices. We have developed a top-down approach for fabricating ordered arrays of high quality GaN-based nanorods with controllable height, pitch and diameter. This approach avoids many of the limitations of bottom-up synthesis methods. In addition to GaN nanorods, the fabrication and characterization of both axial and radial-type GaN/InGaN nanorod LEDs have been achieved. The precise control over nanorod geometry achiveable by this technique also enables single-mode single nanowire lasing with linewidths of less than 0.1 nm and low lasing thresholds of ∼250kW/cm 2. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

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TYPE Conference YEAR 2012
ScopusOSTI

Optical performance of top-down fabricated InGaN/GaN nanorod light emitting diode arrays

Optics Express

Li, Qiming L.; Crawford, Mary H.; Koleske, Daniel K.; Figiel, J.J.; Cross, Karen C.; Wang, George T.

Vertically aligned InGaN/GaN nanorod light emitting diode (LED) arrays were created from planar LED structures using a new top-down fabrication technique consisting of a plasma etch followed by an anisotropic wet etch. The wet etch results in straight, smooth, well-faceted nanorods with controllable diameters and removes the plasma etch damage. 94% of the nanorod LEDs are dislocation-free and a reduced quantum confined Stark effect is observed due to reduced piezoelectric fields. Despite these advantages, the IQE of the nanorod LEDs measured by photoluminescence is comparable to the planar LED, perhaps due to inefficient thermal transport and enhanced nonradiative surface recombination.

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TYPE Journal Article YEAR 2011
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A revolution in micropower : the catalytic nanodiode

Creighton, J.R.; Baucom, Kevin C.; Coltrin, Michael E.; Figiel, J.J.; Cross, Karen C.; Koleske, Daniel K.; Pawlowski, Roger P.; Heller, Edwin J.; Bogart, Katherine B.; Coker, Eric N.

Our ability to field useful, nano-enabled microsystems that capitalize on recent advances in sensor technology is severely limited by the energy density of available power sources. The catalytic nanodiode (reported by Somorjai's group at Berkeley in 2005) was potentially an alternative revolutionary source of micropower. Their first reports claimed that a sizable fraction of the chemical energy may be harvested via hot electrons (a 'chemicurrent') that are created by the catalytic chemical reaction. We fabricated and tested Pt/GaN nanodiodes, which eventually produced currents up to several microamps. Our best reaction yields (electrons/CO{sub 2}) were on the order of 10{sup -3}; well below the 75% values first reported by Somorjai (we note they have also been unable to reproduce their early results). Over the course of this Project we have determined that the whole concept of 'chemicurrent', in fact, may be an illusion. Our results conclusively demonstrate that the current measured from our nanodiodes is derived from a thermoelectric voltage; we have found no credible evidence for true chemicurrent. Unfortunately this means that the catalytic nanodiode has no future as a micropower source.

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TYPE SAND Report YEAR 2010
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Final LDRD report : development of advanced UV light emitters and biological agent detection strategies

Crawford, Mary H.; Armstrong, Andrew A.; Allerman, A.A.; Figiel, J.J.; Schmitt, Randal L.; Serkland, Darwin K.

We present the results of a three year LDRD project which has focused on the development of novel, compact, ultraviolet solid-state sources and fluorescence-based sensing platforms that apply such devices to the sensing of biological and nuclear materials. We describe our development of 270-280 nm AlGaN-based semiconductor UV LEDs with performance suitable for evaluation in biosensor platforms as well as our development efforts towards the realization of a 340 nm AlGaN-based laser diode technology. We further review our sensor development efforts, including evaluation of the efficacy of using modulated LED excitation and phase sensitive detection techniques for fluorescence detection of bio molecules and uranyl-containing compounds.

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TYPE SAND Report YEAR 2007
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Results 51–75 of 84
Results 51–75 of 84