Quantum transistors and circuits break through the barriers

Resonant tunneling diodes and transistors, which are ´vertical´ quantum devices, in which the current flows perpendicular to the layers instead of along them, are discussed. The operation of both devices is explained. Various types of resonant tunneling transistor are examined, with particular attention to multistate devices. Applications to frequency multipliers, parity generators, and analog-to-digital converters are presented.<>