August 26, 2008: IBM says it has integrated and controlled an electrically driven light emitter based on a single carbon nanotube, which it says is a first step in developing nanotube-based integrated electronic and nanophotonic devices. The research is described in the Aug. 25 issue of the journal Nature Nanotechnology.
Semiconducting single-walled carbon nanotubes have a direct, diameter-dependent bandgap and can be exited readily by current injection, making them attractive as nano-emitters with spectrally broad and spatially nondirectional electroluminescence and low radiative yield, note the researchers from IBM’s TJ Watson Research Center in Yorktown Heights, NY.
Their work involves combining a single nanotube-based field-effect transistor (FET) with a pair of metallic nanomirrors on a chip. They were then able to control the optical emission properties from the 2nm-dia. nanotube including emission wavelength, spectral and spatial distribution of emitted light, and efficiency of emission, displaying “an unprecedented level of control over electrically-driven light nano-emitters.” The spectral full-width at half-maximum of the emission was reduced from ~300nm to ~40nm at a cavity resonance of 1.75μm, and the emission becomes highly directional, they report. The maximum enhancement of the radiative rate was estimated to be 4, and both the optically and electrically excited luminescence of single-walled nanotubes involved the same E11 excitonic transition.
The work demonstrates the concept of a “cavity-controlled” light source, where emission from optically active materials is controlled using an optical cavity, where light is bounced back and forth and interacts with active materials. A laser is one example of such a structure; now, nano-cavities are shown to control and improve properties of individual, single-walled carbon nanotubes, indicating they might be used in integrated nanophotonic circuits, quantum optics, and high-performance on-chip optical interconnects and sensors.
Building an optical cavity around the light-emitting nanotube mirrors (see bottom and top), IBM scientists were able to confine wavelengths to the desired 1.55μm communications frequency. (Source: IBM)