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12 Physics Semiconductor Electronics: Materials, Devices And Simple Circuits - Set No : 67 Question No :7

Question No : 7
               Why is there sudden increase in current in zener diode?     

                a)          Due to rupture of bonds          b)          Resistance of depletion layer becomes less     

                c)          Due to high doping          d)          None of the above     

Answer No : 7
     (a)The reverse bias potential that results in this sudden change in characteristics is called the zener potential and is given by the symbol  When the voltage across diode is increased in the reverse bias region, the minority carriers gain velocity and associated kinetic energy. These minority carriers are responsible for the reverse saturation current. The collisions of these minority carriers with atomic structure will result in an ionisation process and a very high current is established. This current is called avalanche current and the region in which this current is established is called avalanche breakdown region. The magnitude of zener potential may be decreased by increasing doping levels in the  and -type materials.When the decreases to a very low level, there is a strong electric field in the region of the junction that can break the bonds with C in the atom and generate charge carriers. This mechanism is called zener breakdown.     

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