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Silicon rivals GaAs emission efficiency

30 Oct 2002

The efficiency of silicon-based light emitters can now match that of materials such as gallium arsenide.

Researchers at STMicroelectronics, the French-based chipmaker, have unveiled silicon-based light emitters with efficiencies matching those of traditional compound semiconductor materials, such as gallium arsenide (GaAs). The company says its innovation will enable optical and electrical functions to be combined on the same silicon chip for the first time.

Although silicon is ideal for building microprocessors, memory devices and other complex circuits, it has not until now been made to act as an efficient light emitter. Engineering samples of the devices will be available by the end of 2002.

"The ability to combine optical and electronic processing on the same chip presents enormous opportunities for ST to be the first to develop many new types of semiconductor products, especially as the technology is compatible with existing volume production process flows and equipment," said GianGuido Rizzotto, the director of R&D at STMicroelectronics. "Key manufacturing issues have already been solved so that the technology can be rapidly moved into production."

ST's technology exploits an novel structure in which ions of rare-earth metals such as erbium or cerium are implanted in a layer of so-called silicon-rich oxide - in other words, silicon dioxide enriched with silicon nanocrystals 1-2 nm in diameter. The frequency of the emitted light depends on the rare-earth dopant exploited in the process.

"The quantum efficiencies achieved are about 100 times better than has previously been possible with silicon," said Salvo Coffa, manager of the team responsible for the breakthrough. "The efficiency is, for the first time, comparable to that obtained from GaAs and other compound semiconductors traditionally used to make light-emitting diodes."

The new technology was developed at ST's Corporate Technology R&D Organization in Catania, Sicily, using the same pilot line that the company exploits to develop advanced semiconductor devices. This has allowed the ST to accelerate the transfer from proof-of-concept experiments to prototype development and industrialization.

One of the first applications of the new technology will be power-control devices in which the control circuitry is electrically isolated from the power-switching transistors. ST is also investigating integrated optical data-transmission systems for use in advanced electronic circuits, as well as low-cost integrated devices for dense wavelength division multiplexing systems.

Susan Curtis is editor of fibers.org.

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