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ST readies silicon emitters for market

25 Sep 2003

Light-emitting silicon devices will hit the shelves within the next six months.

Silicon light-emitting technology will enter the market in 2004, according to chip-maker STMicroelectronics.

Having announced silicon-based light emitters with efficiencies matching those of compound semiconductor materials last October, the company says it has made significant advances and is now preparing to release commercial products. It’s first offering will be an optocoupler, an optical switch made from an LED and a photodetector that uses light to couple together two sides of the electrical world.

Electronic circuits are typically made from silicon, a material not renowned for its light-emitting properties. This has traditionally forced optoelectronic devices makers to use semiconductors such as gallium arsenide, which is notoriously hard to integrate onto silicon. ST's research means that compatibility problems such as these could soon be a thing of the past.

“ST has made substantial further progress towards turning this pioneering research into near-term commercial products,” said Salvo Coffa, researcher director at ST. “Comparing the performance of our first prototypes with that of existing technology, we expect to reach the commercial crossover point in around six months.”

ST is also optimistic that it can improve the performance of its current second-generation devices. “We will be ready with our third-generation LED with a factor 10 further increase in maximum emitter power [in the next year],” a spokesperson for ST told Optics.org.

To date, the company has developed devices emitting in the green and the near infrared. According to ST, its second generation LEDs are electrically pumped and emit more than 1 mW of light for each square millimeter of silicon.

In recent years, scientists have tried many approaches to coax light out of silicon. One approach involves etching microscopic holes into bulk silicon making it porous. ST’s trick is to use a structure in which ions of rare-earth metals such as erbium or cerium are implanted in a layer of silicon dioxide enriched with silicon nanocrystals. The company says the key to the improved performance is a better depth distribution of the rare-earth ions in the dielectric layer and an optimized annealing step.

Compared with the first-generation prototypes that ST announced in October 2002, the firm says that the quantum efficiency of its second-generation devices has gone up by 50% and the output power has increased by a factor of 50. Having reached these levels, ST is confident that it will enter the optocoupler market in 2004 with products that are similarly priced or cheaper than existing components.

Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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