news digest ♦ LEDs


the typical use of halogen and compact fluorescent downlights in these areas of the hotel.


“We selected Bridgelux LED arrays as the light source for our luminaires because they deliver the high quality of light and product reliability demanded by both our company and the Sheraton Hotel’s rigorous lighting standards,” explained John Cho, President of Ilsung Moolsan.


“The Bridgelux arrays offer a high quality, highly cost-effective and easy to integrate solution while providing the beautiful, natural warm white light required for this high-end hotel environment,” he continued.


Bridgelux provides one of the industry’s broadest ranges of high quality, high performance LED light sources. The firm’s LED chips enable lighting OEMs to expand their portfolios of energy efficient lighting products to satisfy the power saving requirements without sacrificing light quality.


The firm hopes to help rapidly transform the lighting Industry and to support government-led programs such as the Korean Government’s “LED Lighting 2060 Plan,” announced in June to promote greater energy efficiency by increasing the use of LED lighting.


“Bridgelux is very pleased to have been selected by Ilsung Moolsan to provide the solid state light source for their down lights,” said Jim Miller, chief sales and marketing officer at Bridgelux. “The collaboration between Ilsung Moolsan and the Sheraton organisation is an outstanding example for any hotel looking to gain significant and immediate savings. Switching to LED lighting now offers not only energy savings and maintenance avoidance, but also delivers the quality of light demanded by even the top hotels in the industry.”


Zinc Oxide microwires enhance LEDs


By using a piezoelectric material alongside a gallium nitride LED, the external efficiency can be amplified by a factor of more than four times.


Scientists have used zinc oxide microwires to significantly improve the efficiency at which GaN


88 www.compoundsemiconductor.net November/December 2011 LEDs convert electricity to ultraviolet light.


The devices are believed to be the first LEDs whose performance has been enhanced by the creation of an electrical charge in a piezoelectric material using the piezo-phototronic effect.


By applying mechanical strain to the microwires, researchers at the Georgia Institute of Technology created a piezoelectric potential in the wires, and that potential was used to tune the charge transport and enhance carrier injection in the LEDs.


This control of an optoelectronic device with piezoelectric potential, known as piezo-phototronics, represents another example of how materials that have both piezoelectric and semiconducting properties can be controlled mechanically.


Studying LEDs


Zhong Lin Wang (right) and Ying Liu study LEDs whose performance has been enhanced through the piezo-phototronic effect. (Georgia Tech Photo: Gary Meek)


“By utilising this effect, we can enhance the external efficiency of these devices by a factor of more than four times, up to eight percent,” said Zhong Lin Wang, a Regents professor in the Georgia Tech School of Materials Science and Engineering. “From a practical standpoint, this new effect could have many impacts for electro-optical processes - including improvements in the energy efficiency of lighting devices.”


Because of the polarisation of ions in the crystals of piezoelectric materials such as ZnO, mechanically compressing or otherwise straining structures made from the materials creates a piezoelectric potential - an electrical charge. In the GaN LEDs, the researchers used the local piezoelectric potential to tune the charge transport at thep-n junction.


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