# Volt-Ampere Characteristic of a PN Junction Diode

Volt-ampere or V-I characteristics of PN junction diode is the curve between voltage across the junction and the circuit current. Usually voltage is taken along x-axis and current along y-axis.

The figure below shows circuit arrangement for determining the V-I characteristics of a PN junction diode. The characteristics can be studied under three heads i.e.

1. Zero external voltage
2. Forward bias
3. Reverse bias ## 1.Zero external voltage:

When the external voltage is Zero, i.e circuit is open at K ,the potential barrier at the junction does not permit current flow. The circuit current in this case is indicated by the point O in figure.

## 2.Forward bias:

With the forward bias to the PN junction diode i.e. p -type connected to positive terminal and n-type connected to negative terminal, the potential barrier is reduced. when the potential barrier eliminates at certain voltage current starts to flow in the circuit. The current increases with the increase in forward voltage. Thus the rising curve OB is obtained with forward bias. Form the figure OA ,the current increases very slowly and the curve is non-linear because the external voltage is used in overcoming the potential barrier. Once the external voltage exceeds the potential barrier voltage, the PN junction  diode behaves like an ordinary conductor. Therefore the current starts to rises very sharply with increase in external voltage(AB) and is almost linear. ## 3.Reverse bias

With the reverse bias to the PN junction diode i.e. p -type connected to negative terminal and n-type connected to positive terminal, the potential barrier is increased at the diode junction. There is no flow of current as the junction resistance becomes very high. A very small current(μA) flows in the circuit with reverse bias. This current is due to the minority charge carries.

There are a few free electrons in p-type material and a few hole in n-type material. These undesirable free electrons in p-type and holes in n-type are called minority carriers. For the minority carriers, the applied reverse bias appears as forward bias. Therefore ,a small current flows in the reverse direction.

If reverse voltage is increased continuously, the kinetic energy of electrons(minority carriers) may become high enough too knock out electrons form the semiconductor atoms. At this stage, breakdown of the junction occurs, characterized by a sudden rise of reverse current and a sudden fall of the resistance of barrier region which may destroy the junction permanently.

The forward current through a PN junction is due to the majority carriers produced by the impurity. But the reverse current is due to the minority carriers produced due to breaking of some covalent bonds at room temperature.