Monday, November 21, 2005

"NANOTECH: Nano transistors light the way to all-optical silicon chips"

An experimental light-emitting nanotube (LEN) transistor that's said to achieve 10,000 times the photon flux and over 1000 times the efficiency of LEDs could put researchers closer to the goal of "computing with light." By emitting thousands of photons for the same energy expenditure as one photon emission in an LED, the unipolar carbon nanotube transistor could lead to optical silicon chips, said its creator, IBM Corp. Light emission in solid-state LEDs occurs when separately injected electrons and holes recombine in an exotic material such as gallium arsenide. The resultant drop in energy causes a single photon to be emitted to compensate. IBM had earlier reported an ambipolar nanotube transistor, billed at the time as the world's smallest solid-state emitter, for which hot carriers — electrons and holes — were injected separately into the source and drain. The new technique induces electroluminescence from a single type of carrier — an exciton — using a unipolar nanotube transistor that the company says is three orders of magnitude more efficient than the ambipolar transistor. IBM believes light-emitting nanotube transistors will revolutionize the communications industry by enabling silicon devices to perform both electronic and optical signal processing operations. Eventually all-optical silicon chips could result, but in the meantime silicon chips could perform electrical-to-optical conversions, reducing the need for separate devices made from exotic materials, IBM researchers believe.