Forward Bias p n Junction

A p n junction is said to be operating under the biasing condition it is connected across an electric supply. The Potential difference across the p n junction can be applied in two ways, namely Forward Biasing and Reverse Biasing.

When the positive terminal of a DC source or battery is connected to p-type, and the negative terminal to n-type semiconductor of a pn junction as shown in the figure below, the junction is said to be in Forward Bias condition.

FORWARD-BIAS-P-N-JUNCTION-FIG

The applied forward potential establishes an electric field which reduces the field created due to potential barrier. Thus, potential barrier at the junction is reduced. A forward voltage is sufficient to eliminate the barrier because the voltage of the potential barrier is very small. (0.7 V for silicon and 0.3 V for germanium).

Once the potential barrier is eliminated, a conducting path is established for the flow of current. Thus, a large current starts flowing through the junction. This current is called as Forward Current.

The external voltage applied to a p n junction that cancels the potential barrier to constitute an easy flow of current through it is called Forward Biasing.

When the p n junction is forward biased the following points are important. They are as follows:-

  • The junction potential barrier is reduced and at some forward voltage, it is eliminated.
  • The junction offers low resistance, known as Forward Resistance (Rf) to the flow of current through it.
  • The magnitude of flow of the current through the circuit depends upon the applied forward voltage.

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