The Tiniest Solid-State Light Emitter

The tiniest solid-state light emitter, produced by Phaedon Avouris and his colleagues at IBM, consists of a single-walled carbon nanotube (NT) strung between two electrodes, and controlled by a third. The business part of this minuscule transistor is a nanotube only 1.4 nm wide and tailored to be semiconducting. In this arena electrons coming from one electrode meet with positively charged "holes" coming from the other electrode. When the two species meet they combine and emit a tiny burst of light. This light is conveniently engineered to be at a wavelength of 1.5 microns, invisible to the human eye but perfect for photonic applications. Why use a NT when a larger piece of bulk semiconductor could also produce light? Because of the potentially much greater energy efficiency and compactness of the light emitting region. Single-molecule light emission has been instigated before, but not under the auspices of solid state wiring. The NT wire also seems to be robust: it is able to carry 6 micro-amps of current, for a current density of more than 100 million amps per square cm. (Misewich et al., Science 2 May 2003.)