Researchers from IBM (Yorktown Heights, NY) and Duke University (Durham, NC) have produced bright IR electroluminescence at local electric fields in the junction between suspended and supported parts of a partially suspended single-carbon-nanotube field-effect transistor in unipolar operation. Unlike light-emitting diodes or ambipolar carbon-nanotube field-effect transistors, in which electrons and holes are injected from source and drain electrodes separately, the unipolar device in the IBM-Duke experiment generated carriers locally when either electrons or holes were accelerated by electrical forces great enough to create strongly correlated electron-hole pairs.
The local unipolar mechanism led to a two- to three-orders-of-magnitude increase in electroluminescent efficiency over light emission by ambipolar carbon-nanotube field-effect transistors. The researchers attributed the effect to weak electron-phonon scattering and strong electron-hole binding caused by 1-D confinement. The combination of extraordinary current carrying and ultrasmall size in the carbon nanotube led to an ultrabright light source; the high excitation density allowed the researchers to observe emission from highly excited states that were not observable through photo-excitation. Contact Phaedon Avouris at [email protected].