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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
OSTIDOI

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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Carrier recombination mechanisms and efficiency droop in GaInN/GaN light-emitting diodes

Applied Physics Letters

Crawford, Mary H.; Koleske, Daniel K.

In this work, we model the carrier recombination mechanisms in GaInN/GaN light-emitting diodes as R=An+Bn2+Cn3+f(n), where f(n) represents carrier leakage out of the active region. The term f(n) is expanded into a power series and shown to have higher-than-third-order contributions to the recombination. The total third-order nonradiative coefficient (which may include an f(n) leakage contribution and an Auger contribution) is found to be 8×10-29 cm6 s-1. Finally, comparison of the theoretical ABC+f(n) model with experimental data shows that a good fit requires the inclusion of the f(n) term.

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TYPE Journal Article YEAR 2010
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Results 101–125 of 202
Results 101–125 of 202