IBM Produces Infrared Emitting Nanotubes
Electrical measurements suggest that the emission comes from radiative recombination of electrons and holes simultaneously injected into the undoped nanotube. The team believe their results are consistent with a model where thin Schottky barriers are formed at the source and drain contacts of the nanotube FET.
The hope is that such a recombination source may form the basis for ultra-small integrated photonic devices. Unipolar devices, with only one carrier type (electron or hole), failed to emit light.
The semiconducting single-walled carbon nanotubes (s-SWNTs) measure 1.4nm in diameter. The research team detected light with a wavelength of around 1500nm - in the range of wavelengths widely used in optical communications. The device bandgap (about 750meV) corresponds to a 1650nm wavelength.
Given an inverse proportionality between tube diameter and bandgap, the researchers expect to be able to control the emitted wavelength. Improved injection efficiency and emission along with reduced operating voltage are expected to result from aggressive scaling of the gate oxide thickness and use of a high dielectric constant insulator.
The Schottky model suggests maximum emission with a gate voltage (Vg) being half the drain (Vd of 4V and 8V). Emission should increase at higher Vd. The model fits very well the observed intensity, but the researchers say this could be "fortuitous". An alternative model based on the product of electron and hole currents gave a poor intensity description but fitted the peak width well.
