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Contents - Winter 2008

Vol. 1 No. 1

Ionic Alchemy—Generating Energy and Light with Silicon

By Mari-Louise Rowley

Ancient alchemists dreamt of making gold out of lead. Michael Bradley is close to achieving transformations that would indeed be worth their weight in gold.

The University of Saskatchewan physicist is developing techniques to change the properties of silicon—a common natural element—which could lead to more efficient sources of light and energy, and to much faster computers and communications.

“Silicon is abundant, non-toxic and inexpensive, so basically anything that we can do with silicon has a good chance of getting to market,” Bradley says.

Using a plasma-based technique called ion implantation, Bradley and his team have successfully made silicon that emits light—in effect, creating a new material in the process.

But if silicon is such an excellent semiconductor already, why change it? “Whenever an electron travels through a semiconductor, it can either go along unimpeded and lose energy through heat—think of an overheated computer. Or it can make a big— quantum—jump and lose energy by emitting a photon,” explains Bradley. A photon is an elementary particle of light.

One application for implanted silicon is inexpensive and energy-efficient light walls for homes and offices. These could potentially be tuned to simulate full-spectrum sunlight for people who can’t tolerate fluorescent light. Bradley is collaborating with Julie Thompson, a scientist at the Canadian Light Source (CLS) synchrotron, to explore what happens at the molecular level to enable silicon to emit light.

“If we can put electricity into this new material and get light out, then we should be able to put sunlight in and get electricity,” Bradley says.

If this idea works, implanted silicon could be used to make more efficient solar cells, reducing costs by a factor of 10 or more.

Bradley’s research is at the cutting edge of photonics, where all communications technology is heading. In electronics, the electron is the carrier of information, whereas the photon is the carrier of information in photonics, he says.

The benefit of using photons instead of electrons in communications is that they travel faster—as fast as light—providing a higher rate of data transmission and faster computation. How much faster would you be able to download a movie to DVD, for example? Today it could take 45 seconds with a high-speed FireWire connection, but with optical data transmission, a movie download would take about four milliseconds.

The convergence of electronics with photonics has many challenges. But for Bradley, they are opportunities.

For example, all computer chips are made of silicon wafers. To send data using fibre optics, a laser is needed to convert electrical signals into photon-based optical signals. And these lasers are not made of silicon, but of exotic and expensive semiconductor materials that are difficult to integrate with silicon. This problem would be solved if the lasers themselves could be made from silicon.

Silicon-based lasers are the contemporary alchemist’s—and Bradley’s—dream. “We don’t yet know if this is possible, but if we find that it is, the world would beat a path to our door.”