Cuprous halides: The key ingredient for cheap, ultra-efficient LEDs?
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Nov 26, 2013
To propel widespread uptake of solid-state lighting, LEDs must be cheaper and more efficient. One way to do that is to switch the material used to make these devices from nitrides to cuprous halides, which have incredibly high exciton binding energies and can be grown on silicon substrates, argue Doyeol Ahn from the University of Seoul, Korea, and Seoung-Hwan Park from Catholic University of Daegu, Korea.
Isn’t it time to get serious about standards?
Nov 18, 2013
Spec sheets can indicate identical compositions of a layer in a particular structure produced by different suppliers. But in practice there will be variations associated with in-house measurements, calibration samples, and data interpretation. Far greater consistency is possible, however, with an expanding portfolio of true reference samples that are already available, argues Kris Bertness from NIST.
Diminishing droop with superior electron-blocking layers
Nov 15, 2013
It is very tricky to come up with a watertight explanation for the cause of droop. However, it is certainly possible to combat this mysterious malady, which causes LED efficiency to decrease at high current densities, by: turning to better electron-blocking layers made from InAlN; and improving the injection of holes into the wells, plus their distribution throughout the active region, argues to Jae-Hyun Ryou from the University of Houston, Russell Dupuis and P. Douglas Yoder from Georgia Institute of Technology and Fernando Ponce from Arizona State University.
Building brighter and cheaper UV LEDs
Nov 06, 2013
It is far more challenging to make a bright, cheap ultra-violet LED than one emitting in the blue. But success is promised with a transparent contact layer, reflective electrodes, photonic structures and growth on silicon, says Hideki Hirayama from RIKEN.
Pursuing pathways to widespread adoption of solid-state lighting
Oct 28, 2013
The solid-state lighting revolution will be spurred by plummeting LED costs and improvements to the quality of emitted light. Success on these fronts could be aided by refinements to existing technologies; the introduction of GaN-on-silicon LEDs; a move to colour mixing of red, green and blue LEDs; and a switch from LEDs to lasers at the primary lighting source. All options were discussed at the International Conference on Nitride Semiconductors. Richard Stevenson reports
Cranking up the efficacy of Green LEDs
Oct 21, 2013
Green LEDs don't deliver the same level of performance as their red and blue cousins. However, by decreasing the current density with a larger chip and optimising growth conditions to reduce dark spots it is possible to close that gap with LEDs that hit 190 lumens per watt at a 100 mA drive current, says Osram’s Andreas Löffler and Michael Binder.
Slashing defect densities in nitride films grown by high temperature ammonia MBE
Oct 17, 2013
Grown in an MOCVD reactor, nitride films tend to yield fewer defects than when they are formed in MBE chambers. But this gap in material quality can disappear with high-temperature ammonia MBE, which produces epitaxial structures with outstanding electrical characteristics, argues Alexey Alexeev and Stanislav Petrov from SemiTEq.
An elemental change to laser design
Oct 07, 2013
Today's telecom lasers are plagued with Auger-related losses, which drive down efficiency and make device cooling mandatory. The solution: Switch to an active region with alloys featuring a bismuth content of more than 10 percent, claim members of the European team BIANCHO.
Water-based strippers tread lightly on the environment
Oct 03, 2013
A novel, water-based stripper offers a fast, environmentally friendly approach to high quality removal of photoresist and the carrying out of metal lift-off, claims Dirk Schumann from Bubbles & Beyond.
Boosting triple-junction yield with in-situ monitoring
Sep 30, 2013
In-situ monitoring provides a great deal of valuable information for developers and producers of multi-junction solar cells. It can determine interface quality; the thickness, doping level and composition of every layer; and wafer bow, says Oliver Schulz from LayTec.
Building brighter, cheaper LEDs
Sep 26, 2013
The gases and chemicals that are consumed during the manufacturing of LEDs make a considerable contribution to device costs. But savings are possible by switching to a new MOCVD design with a flared chamber profile. This not only trims gas consumption by up to 40 percent but also shortens the growth interruption between layers, leading to improved multiple quantum well quality, say Frank Campanale, Mike Begarney and Tom Ryan from Valence Process Equipment.
GaN in power electronics applications
Sep 23, 2013
Bandgap materials GaN and SiC are generating significant buzz globally. Strategy Analytics expects SiC to be the primary replacement technology for silicon power devices, while GaN seeks initial commercial traction in applications with breakdown voltages of less than < 600V and power requirements of less than 5kW
Simplifying air quality monitoring
Sep 16, 2013
Conventional sensors for assessing the air quality in buildings are wired into the mains, making them expensive to install and reposition. But portability and battery powering is possible with Gas Sensing Solutions’ modules that feature mid-infrared LEDs and photodetectors. Richard Stevenson reports.
Replacing halogen lamps
Sep 10, 2013
Inferior light quality holds back the sales of most LEDbased replacements for halogen lamps in casinos, hotels, high-end retailers and cruise ships. But that’s not the case for Soraa’s lighting products, which produce full-spectrum emission with a violet LED pumping red, green and blue phosphors. Richard Stevenson reports.
Germanium virtual substrates: a promising platform for multi-junction solar cells
Aug 19, 2013
Cutting cell costs will ensure that concentrating photovoltaic systems become more competitive. One way to do this is to turn to silicon substrates incorporating germanium-based layers, which bridge lattice constants and allow the formation of a 1 eV junction for boosting efficiency, say Andrew Clark, David Williams and Radek Roucka from Translucent.
Uniting silicon and InP to make versatile, low-cost photonic chips
Aug 15, 2013
Telecom and datacom networks are under ever-increasing strain from an explosion in data transfer. What’s the long-term solution? It’s a universal photonics technology that marries InP performance with large silicon wafers, argue Daniel Sparacin and Greg Fish from Aurrion.
Preparing GaN for greater military service
Aug 13, 2013
The US Department of Defense views GaN MMICs as too expensive and insufficiently reliable for its needs. To address these shortcomings, it is spearheading a project to drive down cycle times, increase yield and improve reliability. Richard Stevenson reports.
Scarcity claim is scaremongering
Aug 07, 2013
Rumours are circulating that reserves of indium could soon run out, threatening the production of displays, LEDs, and lasers. But if you take a hard look at the evidence, you’ll find that the naysayers are ill-informed and there is plenty indium to go round for many decades, argues Malcolm Harrower from Indium Corporation.
Driving SiC switches
July 29, 2013
Engineers can build motor drives and power supplies that deliver very high levels of efficiency by combining frugal, fast SiC Super Junction Transistors with optimised gate drivers, argues Ranbir Singh from GeneSiC Semiconductor.
A unified theory for LED droop
July 29, 2013
What causes droop, the decline in an LED’s efficiency as the current passing through it is cranked up? Is it Auger recombination, or could it be carrier leakage? Both of these camps are dismissive of the other’s ideas, but maybe they shouldn’t be, because it is possible that it is the interplay between these two processes that gives a deeper insight into droop, suggest Marcus Deppner, Friedhard Römer and Bernd Witzigmann from the University of Kassel, Germany.
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