How depletion region across zener diode gets thin?

Answer 1

A diode is basically a PN junction device. P type semiconductors are rich in holes while N types are rich in electrons. (Rich means majority carriers here, which are found in the outer shell of atoms).

Thus at the junction of this P and N type material, electrons and holes will combine resulting in a deficiency of charge carriers. This is termed the depletion region.

When you attach the negative terminal of a battery to the N end of the diode and the positive terminal to the P end, the electrons will be repelled towards the junction and holes too will move towards the junction region, making it thin (narrow) (Further increase in voltage will make current to pass through). The opposite occurs when they are connected the other way. The region becomes thin.

For normal operations, zener diodes are connected in reverse (diodes usually are connected reversely unless you want drop some voltage) the depletion layer widens, as described above. But at a certain reverse voltage, the zener starts to conduct suddenly. This is called avalanche/breakdown voltage. How the layer becomes thin (if at all, seems improbable) when they are reverse connected, I do not know.

Answer 2

Doping is a process of mixing sum impurity in a iinsulator and then that acts like conductor...The materials which are said to behave like this are called semi conductor . it is very often to know that when we add some impurity ,the bonding inside the semi conductor just breaks and rejoins itself with new commer electrons of the impurity...major semi conductors are GaAs,Si,Ge ...we can notice out that if 1 electron is added to silicon(si),it reffers to a conductivity of 10 million electrons...so just think of this example,when we add extra impurity...what would happen?????????resulting a great vacancy for electrons to continueue their activities. Coming to depletion region...it is just a smaal region where ions are formed + on N types and - to P Types .though it is very small but it cannot be neglected ....Hence we improve the ratio of impurity added.....the free electrons available are also in a huge number so a litttle space for the Depletion region remains there but it never ends....i-e depletion region can not be removed finally