The Zener Effect

Zener Diode

The zener diode uses a p-n junction in reverse bias to make use of the zener effect, which is a breakdown phenomenon which holds the voltage close to a constant value called the zener voltage. It is useful in zener regulators to provide a more constant voltage, for improvement of regulated power supplies, and for limiter applications. 齐纳二极管利用反向偏置的p-n结来利用齐纳效应，这是一种击穿现象，可以使电压接近一个称为齐纳电压的常数值。它在齐纳稳压器中用于提供更稳定的电压，以改进稳压电源，并用于限幅应用。

Tunnel Diode Characteristic

In 1957, Esaki, Kurose and Suzuki discovered that quantum mechanical tunneling of electrons could be achieved in a solid state diode. Josephson had discovered tunneling characteristics in the Josephson junction for superconductors. Esaki and Josephson shared the 1973 Nobel Prize for these discoveries.

In the case of the tunnel diode, the conditions for tunneling were achieved by more heavily doping the semiconductors associated with the pn junction. With germanium or gallium arsenide the depletion layer at the junction was very narrow, and permitted electrons to tunnel across the barrier. For very low reverse voltages through small positive voltages, the tunneling increased and the junction acted like a conductor. 在隧道二极管的情况下，通过更 heavily doping 与 pn 结相关的半导体，实现了隧道效应。使用锗或砷化镓时，结处的耗尽层非常狭窄，允许电子穿过势垒。对于非常低的反向电压或小的正向电压，隧道效应增强，结 behaves like a conductor。

For small forward bias, electrons tunnel across the depletion region from the P to the N side and fill states in the conduction band on the N-side. They align with hole states on the P-side. With increasing forward voltage, there is increasing misalignment and the current begins to drop with increasing forward voltage, producing a "negative resistance" behavior. For higher forward voltages, the junction begins to act like a normally forward biased diode, but the negative resistance regime was found to be very useful in producing oscillators.

Tunnel diode oscillators were found to be very useful through the 1970s as high-frequency oscillators and found use in the space program. They have since been mostly replaced with a variety of other oscillator types.