Burning brighter
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STMicroelectronics (STM) has revealed details of a technology that allows silicon-based light emitting material to match the efficiency of traditional light-emitting compound semiconductor materials such as gallium arsenide (GaAs).
According to STM, the new technology is based on an innovative structure in which ions of rare-earth metals such as erbium or cerium are implanted in a layer of Silicon Rich Oxide (SRO), i.e. silicon dioxide enriched with silicon nanocrystals with a diameter of 1-2nm.
'The quantum efficiencies achieved are about 100 times better than has previously been possible with silicon and are, for the first time, comparable to those obtained from GaAs and other compound semiconductors traditionally used to make light-emitting diodes,' said Salvo Coffa, manager of the team responsible for the breakthrough. The frequency of the emitted light depends on the choice of rare-earth dopant and ST has patented key techniques for implanting the rare-earth ions into the silicon.
The new technology was developed in Catania, Sicily, by researchers from ST's Corporate Technology R and D Organisation. The process was developed using the same pilot line that ST uses to develop new MOSFET and bipolar devices.
ST plans to build integrated power control devices based on the technology. Currently, electrical isolation, which is mandatory in many applications for safety reasons, can only be achieved by using external devices such as relays, transformers or discrete optocouplers. But using STM's technology, this will no longer be necessary.
ST has already patented a novel structure in which two circuits, built on the same chip but electrically separated from each other by insulating silicon dioxide, communicate via optical signals using integrated silicon light emitters and detectors. Devices based around the structure will have numerous applications in motor control, power supplies and solid-state relays.
Engineering samples will be available by the end of 2002.
