(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. |