IF MICROCHIPS could communicate using light rather than electric current,
they would be able to work at blistering speeds. But until now,
silicon鈥攖he stuff most microchips are made of鈥攈as stubbornly refused
to generate the all-important laser light needed for this to work.
But this week, researchers report that they have finally persuaded the
material to amplify a light beam. While that鈥檚 not enough in itself, it鈥檚 an
achievement that could one day lead to an all-silicon laser. To work like a
laser, excited silicon atoms have to dump photons in unison into a passing light
beam. But until now, excitations in silicon atoms have tended to peter out
before they can give off light.
When an electron in silicon is excited, it gets a boost and leaves behind a
shadowy vacancy, called a hole. For the material to act as a laser, the pair
should recombine to give off light鈥攂ut this rarely happens in silicon,
because the electron and hole wander away from each other. But that problem can
be overcome by confining the electron-hole pair within tiny silicon crystals
only 3 nanometres in diameter, reports Lorenzo Pavesi and his colleagues from
the University of Trento, in Povo, Italy, this week (Nature, vol 408, p
440). 鈥淧airs cannot move away,鈥� Pavesi says, 鈥渟o they鈥檙e forced to
谤别肠辞尘产颈苍别.鈥�
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The Trento team embedded billions of nanocrystals in a piece of pure quartz.
They then shone a strong pump beam and a weaker probe beam through the sample.
After the pump beam excited the nanocrystals, the probe beam became amplified
100-fold. 鈥淚鈥檓 on record as saying that amplification will never be achieved,鈥�
says Philippe Fauchet, an electrical engineer at the University of Rochester in
New York. 鈥淚 am happy to swallow my words.鈥�