{{Short description|Type of electrical breakdown in semiconductors}} [[File:I-V curve for a Zener Diode.svg|thumb|right|320px|The I–V curve for a diode showing avalanche and Zener breakdown. ]] 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 free minority carriers which suddenly increase the reverse current.<ref name=CT>{{Cite web | title = PN junction breakdown characteristics | publisher = Circuits Today | date = August 25, 2009 | url = http://www.circuitstoday.com/pn-junction-breakdown-characteristics | access-date = August 16, 2011}}</ref>
==Mechanism== Under a high reverse-bias voltage, the p-n junction's depletion region widens which leads to a high-strength electric field across the junction.<ref name=Harvard>[http://people.seas.harvard.edu/~jones/es154/lectures/lecture_2/breakdown/breakdown.html "Zener and Avalanche Breakdown/Diodes"] {{Webarchive|url=https://web.archive.org/web/20171107012331/http://people.seas.harvard.edu/~jones/es154/lectures/lecture_2/breakdown/breakdown.html |date=2017-11-07 }}, School of Engineering and Applied Sciences, Harvard University</ref> Sufficiently strong electric fields enable tunneling of electrons across the depletion region of a semiconductor, leading to numerous free charge carriers. This sudden generation of carriers rapidly increases the reverse current and gives rise to the high slope conductance of the Zener diode.
==Relationship to the avalanche effect== The Zener effect is distinct from avalanche breakdown. Avalanche breakdown involves minority carrier electrons in the transition region being accelerated, by the electric field, to energies sufficient for freeing electron-hole pairs via collisions with bound electrons. The Zener and the avalanche effect may occur simultaneously or independently of one another. In general, diode junction breakdowns occurring below 5 volts are caused by the Zener effect, whereas breakdowns occurring above 5 volts are caused by the avalanche effect.<ref>{{Cite journal|last1=Fair|first1=R.B.|last2=Wivell|first2=H.W.|date=May 1976|title=Zener and avalanche breakdown in As-implanted low-voltage Si n-p junctions|journal=IEEE Transactions on Electron Devices|volume=23|issue=5|pages=512–518|doi=10.1109/T-ED.1976.18438|bibcode=1976ITED...23..512F |s2cid=12322965 |issn=1557-9646}}</ref> Breakdowns occurring at voltages close to 5 V are usually caused by some combination of the two effects. Zener breakdown is found to occur at electric field intensity of about {{val|3|e=7|ul=V/m}}.<ref name=CT /> Zener breakdown occurs in heavily doped junctions (p-type semiconductor moderately doped and n-type heavily doped), which produces a narrow depletion region.<ref name="Harvard"/> The avalanche breakdown occurs in lightly doped junctions, which produce a wider depletion region. Temperature increase in the junction increases the contribution of the Zener effect to breakdown, and decreases the contribution of the avalanche effect.
==References== {{reflist}}
Category:Electrical breakdown