IBM claims better LED

PORTLAND, Ore. — IBM Corp. unveiled Thursday (Nov. 17) what is said is the world's first electroluminescent nanotube transistor and claimed it glows 1,000 times brighter than a light-emitting diode with as much as 10,000 times more photon flux.

By emitting thousands of photons in silicon with the same energy expenditure as one photon in gallium arsenide, IBM predicted that carbon nanotube transistors will lead to integrated optics on silicon chips. According to IBM, integrated optics on silicon chips could lower costs, accelerate electronics and mitigate the need for exotic semiconductors like gallium arsenide.

IBM said its technique achieves 1000-fold brighter emissions by electrically stimulating a carbon nanotube suspended over a doped silicon wafer. The resulting excitons are electrically neutral, yet emit infrared light when recombined.

Other research groups have reported light emission by carbon nanotubes stimulated to photoluminescence with a laser. IBM claims its technique uses only electrical stimulation to create an exciton density that is 100-fold larger than photoluminescence in nanotubes.

IBM claimed it achieved very high efficiency with its light-emitting technique, IBM through the extreme confinement within a 2-nm-diameter carbon nanotube suspended from each end over a silicon back gate.

IBM fabricated the light-emitting transistor by etching trenches in a silicon dioxide film on a highly doped silicon wafer. The wafer substrate acted as a back gate to the carbon nanotube transistor. The resulting devices emitted infrared light with strength that was exponentially related to the back gate's drive current.