V-I characteristics of PN junction diode:
If the external voltage applied on the silicon diode is less than 0.7 volts, the silicon diode allows only a small negligible electric current.
* When the external voltage applied on the silicon diode reaches 0.7 volts, the p-n junction diode starts allowing large electric current through it.
* At this point, a small increase in voltage increases the electric current rapidly.
* The forward voltage at which the silicon diode starts allowing large electric current is called cut-in voltage.
* The cut-in voltage for silicon diode is approximately 0.7 volts.
* Due to thermal energy in crystal minority carriers are produced.
* These minority carriers are the electrons and holes pushed towards P-N junction by the negative terminal and positive terminal, respectively.
* Due to the movement of minority carriers, a very little current flows, which is in nano Ampere range (for silicon). This current is called as reverse saturation current.
* When the reverse voltage is increased beyond the limit and the reverse current increases drastically is called as reverse breakdown voltage.
* Diode breakdown occurs by two mechanisms: Avalanche breakdown and Zener breakdown.