10 - Some Novel Devices

Abstract

The cold cathode is a device for electron field emission replacing the hot filament in vacuum electronics. High-power high-frequency devices such as the TWT are still the backbone of the high-power amplifier. Recently, a new type of cold cathode has come on the scene: field emission with resonant tunneling (FERT), a scheme that involves placing a QW structure at the surface of a semiconductor with a fairly low work function such as the GaN. The QW structure consists of a GaAlN barrier, a GaN well, and a second barrier, the vacuum. With a field at the surface, the vacuum is transformed into a triangular barrier at the surface. Electrons emerge from the n+ – GaN tunnel resonantly into the vacuum providing a high current, as well as lowering the work function, because the quantum state is flat across the potential profile allowing the effective work function to be lowered by ∼E1/2; where E1 is the quantum state involved. Infact, the device out performed the design by a huge margin, giving a factor of 5 lower electric field, because it was found that the space charge in the well gives rise to additional lowering of the work function, by eVSC, where VSC is the potential from the space charge ρsc.