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An alternative, which is used for voltage references that need to be highly stable over long periods of time, is to use a Zener diode with a temperature coefficient (TC) of +2 mV/°C (breakdown voltage 6.2–6.3 V) connected in series with a forward-biased silicon diode (or a transistor B-E junction) manufactured on the same chip. [4]
Internal resistance causes "leveling off" of a real diode's I–V curve at high forward bias. The Shockley equation doesn't model this, but adding a resistance in series will. The reverse breakdown region (particularly of interest for Zener diodes) is not modeled by the Shockley equation.
PN junction operation in forward-bias mode, showing reducing depletion width. In forward bias, the p-type is connected with a positive electrical terminal and the n-type is connected with a negative terminal. The panels show energy band diagram, electric field, and net charge density. The built-in potential of the semiconductor varies ...
Band-bending diagram for p–n diode in forward bias. Diffusion drives carriers across the junction. Quasi-Fermi levels and carrier densities in forward biased p–n-diode. The figure assumes recombination is confined to the regions where majority carrier concentration is near the bulk values, which is not accurate when recombination-generation ...
In the Zener diode, the concept of PIV is not applicable. A Zener diode contains a heavily doped p–n junction allowing electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material, such that the reverse voltage is "clamped" to a known value (called the Zener voltage), and avalanche does not ...
For simplicity, diodes may sometimes be assumed to have no voltage drop or resistance when forward-biased and infinite resistance when reverse-biased. But real diodes are better approximated by the Shockley diode equation , which has an more complicated exponential current–voltage relationship called the diode law .
In electronics, the Zener effect (employed most notably in the appropriately named Zener diode) is a type of electrical breakdown, discovered by Clarence Melvin Zener. 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 ...
A PN junction in forward bias mode, the depletion width decreases. Both p and n junctions are doped at a 1e15/cm3 doping level, leading to built-in potential of ~0.59V. Observe the different Quasi Fermi levels for conduction band and valence band in n and p regions (red curves). A depletion region forms instantaneously across a p–n junction.