A little more information about tunnel diode:
Tunnel diode – semiconductor diode characterized by a small thickness of the pn junction, a very high concentration of dopants on both sides and a negative dynamic resistance for a certain range of polarizing voltages. It was invented in 1957 by the Japanese physicist Leo Esaki (hence sometimes it can be named Esaki diode). During research on semiconductor junctions he noticed their thus far unprecedented feature based on the tunnel phenomenon. This phenomenon causes charge carriers move through the narrow barrier layer at a very low voltage.
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