Silicon is ideal for electronic applications, but its inability to emit light has limited its potential for optical processing. Now researchers at STMicroelectronics in Italy have increased silicon’s light-emitting efficiency by a factor of a hundred, making silicon competitive with conventional light-emitting semiconductors such as gallium arsenide. This advance, achieved by adding rare-earth metals to silicon, will allow optical and electrical functions to be combined on a single silicon chip.
Researchers at ST’s Corporate Technology R&D Organisation in Catania, Sicily, carried out the work. They implanted ions of rare-earth metals such as erbium and cerium into a layer of silicon rich oxide (silicon dioxide enriched with silicon nanocrystals 1-2 nanometres in diameter). The frequency of the light emitted by the silicon depended on which metal was chosen.
“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,” says GianGuido Rizzotto, director of Corporate Technology R&D. Rizzotto adds that the company should soon be commercialising its technology as it is compatible with existing production methods and equipment.
ST, the world’s third largest semiconductor manufacturer, is using its technique to improve power control devices, such as power supplies and solid-state relays. In these devices the power circuit needs to be electrically isolated from the control circuit because it experiences much higher voltages, but at present can only be isolated using bulky and expensive external components. In contrast, ST builds the two circuits onto the same chip and places silicon dioxide – an insulator – between them. The circuits then communicate with one another through light-emitters and detectors integrated into the silicon.
ST also plans to use its technology in fibre-optic communications and in optical data-transmission systems for advanced CMOS circuits, where signals are distributed through the chip at light speed.
