TUNNEL DIODES

Another type of diode that can oscillate at microwave frequencies is the tunnel diode, also known as the Esaki diode. It produces a very small amount of rf power.
Tunnel diodes work well as amplifiers in microwave receivers. This is especially true of GaAs devices, which act to increase the amplitudes of weak signals without introducing any unwanted rf noise, or signals of their own that cover a large range of frequencies. (An example of noise is the hiss that you hear in a stereo hi-fi amplifier with the gain turned up and no audio input. The less noise, the better.)