Mechanism of operation of double-barrier resonant-tunneling ocsillators

The effect of negative differential resistance observed in double-barrier quantum-well structures is usually attributed to a resonant Fabry-Perot effect. I propose a different mechanism -- involving a sequential rather than resonant tunneling through the two barriers. The effect does not require the existence of a second tunneling barrier and it should also be observable in various single-barrier structures in which tunneling occurs into a two-dimensional system of electronic states. Moreover, a similar effect should also occur in the tunneling from a 2D electron gas into a 1-D system of states (a "quantum wire"). This effect underlies the operation of a recently proposed three-terminal negative differential transconductance device.