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Technical Insight

LED News (LED News)

Despite all the recent bad news surrounding the GaAs industry its medium-term prospects remain strong, according to Stephen Entwistle and Asif Anwar of Strategy Analytics.
LumiLeds demonstrates high-power LEDs LumiLeds Lighting (San Jose, CA) has announced record results from its high-power monochrome and white InGaN-based LEDs, enabled by a combination of developments in large area, high-current chips, as well as light extraction and packaging. The results build on LumiLeds previous announcements in this area (see Compound Semiconductor December 2000/January 2001, p19). The company will shortly introduce these devices as part of its Luxeon family of high-power LEDs. "These are the most efficient, highest flux, large junction devices in the world," said Frank Steranka, LumiLeds materials R&D and product development manager. "Where the rest of the world is talking about 1 lumen devices, we are exhibiting up to 55 lumen devices in certain colors." LumiLeds say the higher flux devices could find use as backlighting for LCD computer monitors and TVs. The use of LEDs could lend these applications brighter colors than the conventional backlight sources, and better power consumption than a CRT. Flashlights that use single high-power LEDs with outputs of 2550 lm are also expected to be on the market within the next year. One of LumiLeds recent demonstrations was a single white LED with a light output of 17 lm, a value that is four times greater than the best commercially available white LED. This device features high current operation at 350 mA and a forward voltage of just 3.2 V. This is a significant achievement as it is the first single point white LED in the light output range required for general lighting applications such as map lights, airplane reading lights and emergency lighting. A well-controlled single point light source allows lighting designers to construct compact fixtures and couple the light to a single optic in the light fixture. This approach is not possible with conventional 5 mm white LEDs which do not provide enough light on their own, necessitating bulky designs with multiple LEDs. LumiLeds also announced a laboratory demonstration of a 425 nm InGaN LED (250 mA DC operation) with a wallplug efficiency of 25%, exceeding the prev-ious record from Cree Lighting of 22% (see Compound Semiconductor August 2000, p25). The wallplug efficiency is the ratio of the light output against the energy input, and is a measure of the amount of energy required to produce the specified light output level. According to LumiLeds, one of the keys to keeping energy requirements low is to retain a low forward voltage. LumiLeds device can be driven at much higher currents: overall, the new high-power device emits over 200 mW, 10 times higher than previous devices. At a current of 1 A, the company has demonstrated over 525 mW of output power. GELcore meets traffic-light energy standards GELcore (Valley View, OH) has become the first partner of a program set up by the Institute of Traffic Engineers (ITE) to promote energy efficiency. GELcore, which is the joint venture between GE Lighting and Emcore, has certified almost 30 products that meet these performance specifications. These include LED-based traffic lights (see picture), arrow signal confirmation indicators and pedestrian control signs. The ITE produced a set of guidelines for these and other products that meet the US Department of Energy and Environmental Protection Agency standards, under their "Energy Star" program. Cree raises near-UV LED efficiency record Cree Lighting Company (Goleta, CA) has demonstrated a near-UV/violet InGaN LED with a 32% external quantum efficiency. This is the highest known external quantum efficiency reported for an LED in the UV-to-blue portion of the wavelength spectrum, and exceeds Cree s previous result of 28% (see Compound Semiconductor August 2000, p25). High quantum efficiency in UV and near-UV LEDs is essential for driving phosphors to produce efficient white light sources. Cree s LED emits at 390 nm and has a power output of 21 mW (at a current of 20 mA). Ledtronics unveils the latest generation of multicolored LED lamps Ledtronics (Torrance, CA) has announced the development of a new range of lamps employing the latest generation InGaAlP and GaN-on-SiC LEDs in standard 25 mm Edison screw bases. Drawing just 1.01.7 W of power, the DcorLED provides an 11 year life and is available in voltages from 12 to 120 V. Each lamp uses 18 discrete LEDs configured to disperse light in a 270 wide angle or a 30 acute angle. Colors include green (10 cd), white (6 cd), blue (3 cd), yellow (7 cd), red (3.5 cd) and orange (6.5 cd). The company s SurfLED is a surface-mount LED compatible with infrared and convective reflow soldering and pick-and-place automated equipment. At just 1.6 0.8 mm, the device is suitable for backlighting in cell phones, palm pilots and datacom equipment, and has an intensity of 20 mcd. There is also a super bright variant available that produces 60 mcd (20 mA current). Kyma receives SBIR GaN funding boost Crystal growth company Kyma Technologies (Research Triangle Park, NC) has received a Phase II Small Business Innovation Research (SBIR) contract for $750 000 to continue large area GaN bulk crystal growth R&D. Typical substrates for wide bandgap devices include sapphire and two inch SiC. Large area nitride-based wafers would offer manufacturers lower lattice mismatch compared to commonly-used sapphire or SiC substrates, as well as the potential to yield up to four times as many die per wafer by increasing the wafer diameter from two to four inches. To date, the two year old spin-off from North Carolina State University has sampled two and four inch AlN wafers and is also developing GaN substrates (see Compound Semiconductor November 2000, p13). Kyma says it is applying for additional contracts to support these research objectives, with a strong focus on both materials. In more news, Kyma Technologies has welcomed founder and CTO of RF Micro Devices , William Pratt, and former president and CEO of Integrated Silicon Systems, James Poitras, to its board of directors. Infineon powers up new range of SiC applications Infineon (Munich, Germany) is to begin volume production of a new range of SiC Schottky diodes for power applications. SiC enables power devices that block voltages up to 3500 V (more than 10 times that of GaAs) due to a combination of material properties, including a high Schottky barrier, higher electrical breakdown field strength, and the ability to dissipate heat due to a thermal conductivity comparable to copper. These characteristics result in low leakage currents, low on-resistance, and high current densities, offering higher voltage operation in switched mode power supplies and power factor correction for applications such as PCs, servers and base stations. The company s new diodes feature blocking voltages of 300 and 600 V variants in compact transistor outline 220 and TO263 surface-mount packages. As a result of the low switching losses, the diodes can operate at high switching frequencies without complex resonant switching circuits, heat sinks and cooling fans. The development of these devices is discussed in detail on page 45. "An essential advantage of Infineon s SiC technology is that it enables almost loss-free and very fast switching diodes," said Reinhard Ploss of Infineon s Automotive and Industrial business group. "This not only reduces overall losses, but also improves reliability and lowers system costs."
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