Zener breakdown

ZENER BREAKDOWN
In this case breakdown occurs in junctiins, which are heavily doped. When the reverse voltage is increased , the electric field at the junction also increses. A strong electric field causes a covelent bond to break from the crystal structure. As a result a large number of minority carriers are generated and a large current flows though the junction.

What are intrinsic and extrinsic semiconductors ?

The semiconductors are of mainly two types-

(i) intrinsic semiconductor - A semiconductor, which is in its extremely pure form , is known as an intrinsic (or pure) semiconductor. The nature of semiconductors is such that even a small amount of certain impurities can change their electrical properties drastically. It is due to this fact, that a semiconductor would not be called truly intrinsic, unless the impurity level is very small .
The silicon and germanium are two most widely used intrinsic semiconductors.

(i) Extrinsic semiconductors- When a small quantity of impurity is mixed in a pure or intrinsic semiconductor is called the extrinsic semiconductors. The conductivity of resultant crystal depends on the nature and quantity of the impurity added . Depending upon the nature of impurity added in intrinsic semiconductor.
The extrinsic semiconductor are of two types-
    (a) N- type or doner
    (a) P- type or acceptor.

What is semiconductor ?

The materials, whose electrical properties lie between those of conductors and insulators, are know as semiconductor.
The exampels of such materials are-
»cadmium sulphides(CdS),
«gremanium(Ge),
»silicon(Si),
«gallium arsenide(GaAs),
»lead telluride  etc

In terms of energy bands , the semiconductors may be defined as those materials, which at room temperature, have

(i) Partial filled conduction band
(ii)Partial filled valenced band

In semiconductor, at absolute zero temperature there are no electrons in the conduction band and the valence band is completely filled. Thus semiconductors behaves like perfect insulators at 0°K.
However, as the temperature increased, the width of energy gap reduces. Consequently, some of the electrons jump into conduction band and semiconductor show some conductivity. It is thus obvious, that the conductivity of semiconductor increase in temprature.

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