Switchable two-colour light source on a silicon chip

Silicon is an important material for electronic chips and processors, but it has a big drawback: as an indirect semiconductor, it hardly emits any light.

Physicists at the Forschungszentrum Dresden-Rossendorf have managed to make silicon shine red and blue in an alternating fashion. This two-colour light source could help to produce cheap and compact biosensors.

It is not an easy task to make silicon shine or to generate electroluminescence, since in its usual form it can only emit with a very low efficiency.

Initially, the physicists made a blue-violet emitter, which was then the basis of a Silicon based optocoupler. They then demonstrated ultraviolet and green light emitters.

Now the physicists can switch the characteristics of the emitted light between two colours — red and blue, depending on the electrical current flowing through the device.

The compatibility of these emitters with standard silicon microelectronic technology is crucial, since the two-colour nano-switch could easily integrate into common silicon chips.

For the fabrication of the test devices, the group around Dr Wolfgang Skorupa deposits a 100 nanometre thin insulating silicon dioxide layer on the surface of the silicon wafer. Then the element Europium, which belongs to the group of rare-earth elements, is implanted using a beam of fast, charged atoms (ion beam).

Europium forms two different types of impurities carrying a different charge (oxidation state). These are the origin of the red and blue luminescence. Depending on the strength of the electrical current, one or the other impurity type is excited to emit photons.

Possible applications of this two-colour device lie in the area of biosensing. For example, the new silicon-based light source could be used in the fast and cost-effective point-of-care analysis in health and environmental protection.