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A tunnel diode or Esaki diode is a type of ... conduction takes place while the P-N junction is forward biased and blocks current flow when the junction is reverse ...
It occurs in a reverse biased p-n diode when the electric field enables tunneling of electrons from the valence to the conduction band of a semiconductor, leading to numerous free minority carriers which suddenly increase the reverse current. [1]
In semiconductor devices, a backward diode (also called back diode [2]) is a variation on a Zener diode or tunnel diode having a better conduction for small reverse biases (for example –0.1 to –0.6 V) than for forward bias voltages. The reverse current in such a diode is by tunneling, which is also known as the tunnel effect. [3] [4] [5]
The depletion region formed in the diode is very thin (< 1 μm) and the electric field is consequently very high (about 500 kV/m) even for a small reverse bias voltage of about 5 V, allowing electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material.
These can be made to conduct in reverse bias (backward), and are correctly termed reverse breakdown diodes. This effect called Zener breakdown, occurs at a precisely defined voltage, allowing the diode to be used as a precision voltage reference. The term Zener diodes is colloquially applied to several types of breakdown diodes, but strictly ...
When this energy level is higher than that of the electrons, no tunnelling occurs and the diode is in reverse bias. Once the two voltage energies align, the electrons flow like an open wire. As the voltage further increases, tunnelling becomes improbable and the diode acts like a normal diode again before a second energy level becomes ...
Under reverse bias, the diode equation's exponential term is near 0, so the current is near the somewhat constant reverse current value (roughly a picoampere for silicon diodes or a microampere for germanium diodes, [1] although this is obviously a function of size).
Consequently, tunnel diode logic circuits required a means to reset the diode after each logical operation. However, a simple tunnel diode gate offered little isolation between inputs and outputs and had low fan in and fan out. More complex gates, with additional tunnel diodes and bias power supplies, overcame some of these limitations. [7]