What is biasing in P-N junction? What is forward & reverse bias?, What is V-I Characteristic of diode?

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Biasing of a diode- When an external source of energy is applied to a P- N junction, it is called bias voltage or simply biasing. This method either increases or decreases the barrier potential of the junction.There are two types of biasing
(1) Forward bias-  If positive terminal of dc voltage source is connected to P-side & negative terminal is connected to N-side, then diode is said to be forword biased.
A forward voltage is sufficient to eliminate the barrier because the voltage of the potential barrier is very small (0.7V for Silicon & 0.3V for germanium). The complete elimination of the barrier constitutes the low resistance path for the flow of current.This current is called forward current.

(2) Reverse bias- If positive terminal of dc voltage source is connected to N-side & negative terminal is connected to P-side then diode is said to be reverse bias.
The minority carriers, electrons in the P-region & holes in the N region,wander over to the junction and flow towards their majority carrier side giving rise to a small reverse current.This current is known as reverse saturation current.
Reverse saturation current mainly depends upon junction temperature because the major source of minority carriers is thermally broken covalent bonds. For large applied reverse bias, a large number of free electrons are formed which is commonly called as an avalanche of ree electrons.This leads to the breakdown of the junction leading to very large reverse current. The reverse voltage at which the junction breakdown occurs ia known as breakdown Voltage.

V-I Characteristic of a diode- 
When the external voltage is applied on the diode in forward bias. 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 , threshold voltage or knee voltage. The cut in voltage for Ge 0.3V & Si 0.7V.
During the reverse bias, current produced through minority carriers exists known as reverse current.As the reverse voltage increases, this reverse current increases & it suddenly breakdown at point, resulting in the permanent destruction of the junction.

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