An electrical insulator turns metallic within a femtosecond

摘要

State-of-the-art FETs can process electrical signals at rates of about 100 GHz. They can't get much faster than that because of capacitance introduced by electrodes and resistance from the scattering among charge carriers and phonons. But it's also possible to drive carriers ballistically, and all-optical methods for injecting current- no electrodes required-into semiconductors have led to electrical switching on picosecond time scales. Indeed, coherent oscillations of electrons driven by an external electric field were observed in superlattices 20 years ago (see the article by Emilio Mendez and Gerald Bastard in PHYSICS TODAY, June 1993, page 34), though only recently has the capability been extended to bulk semiconductors driven by terahertz pulses.