Is the Esaki diode still used today?
A common misconception is that the Esaki diode is obsolete. While it is no longer a mainstream component in consumer electronics, it remains valuable in specialized applications. The data suggest a remarkable phenomenon: its negative differential resistance allows it to function as a very high-speed oscillator, amplifier, or switch at frequencies exceeding 100 GHz, where conventional transistors struggle. It is used in microwave circuits, radar systems, and some high-frequency test equipment. However, its low output voltage and sensitivity to temperature limit its general use. We must be careful not to overinterpret the theory—the Esaki diode was a proof of concept that quantum tunneling could be exploited practically. Its legacy is more profound in inspiring the field of quantum engineering, including resonant tunneling diodes and superlattice devices, which are actively used in terahertz imaging and quantum cascade lasers. So, while not ubiquitous, it persists in niche roles and as a pedagogical tool.