The response of a diode when connected in an electrical circuit, can be judged from its characteristics known as Volt-Ampere commonly called V-I characteristics. The V-I characteristics in the forward biased and reverse biased condition is the graph of voltage across the diode against the diode current.
The response of p-n junction can be easily indicated with the help of characteristics called V-I characteristics of p-n junction. It is the graph of voltage applied across the p-n junction and the current flowing through the p-
n junction.
The applied voltage is V while the voltage across the diode is Vf. The current flowing in the circuit is the forward current I. The graph of forward current If against the forward voltage Vf across the diode is called forward characteristics of a diode.
Basically forward characteristics can be divided into two regions
1. Region 0 to P As long as Vf is less than cut-in voltage (V , the current flowing is very small. Practically this current is assumed to be zero.
2. Region P to Q and onwards: As V increases towards V the width of depletion region goes on reducing. When Vf exceeds V i.e. cut-in voltage, the depletion region becomes very thin and current I increases suddenly. This increase in the current is exponential as shown in the Fig. by the region P to Q.
The point P, after which the forward current starts increasing exponentially is called knee of the curve.
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