Zener effect
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The Zener effect is a type of electrical breakdown in a reverse biased p-n diode in which the electric field across the diode breaks some of the covalent bonds of the semiconductor atoms leading to a large number of free minority carriers, which suddenly increase the reverse current.[1] Zener breakdown is employed in a Zener diode.
[edit] Mechanism
Under a very high reverse voltage, the p-n junction's depletion region expands leading to a high strength electric field across the junction. This electric field acts to break covalent bonds of the semiconductor atoms which liberates a large number of free minority carriers. This suddenly increases the reverse current and give rise to the high slope resistance of the Zener diode (i.e. the voltage across the diode stays very close to a well defined and constant value, with increasing current).
[edit] Relationship to the avalanche effect
The Zener effect is distinct from avalanche breakdown which involves minority carrier electrons in the transition region which are accelerated by the electric field to energies sufficient to free electron-hole pairs via collisions with bound electrons. Either the Zener or the avalanche effect may occur independently, or both may occur simultaneously. In general, diode junctions which break down below 5 V are caused by the Zener effect, while junctions which experience breakdown above 5 V are caused by the avalanche effect. Intermediate breakdown voltages (around 5V) are usually caused by a combination of the two effects. This Zener breakdown voltage is found to occur at electric field intensity of about 3×107 V/m.[1] Zener breakdown occurs in heavily doped junctions (p-type semiconductor moderately doped and n-type heavily doped), which produces a narrow depletion region. The avalanche breakdown occurs in lightly doped junction, which produces a wider depletion layer. Temperature increases in the junction decrease Zener breakdown and increase the contribution of avalanche breakdown.
[edit] References
- ^ a b "PN junction breakdown characteristics". Circuits Today. August 25 2009. http://www.circuitstoday.com/pn-junction-breakdown-characteristics. Retrieved August 16 2011.
