Forward Biasing of pn junction diode
Forward Biasing of pn junction diode
When the p-side of the junction diode is connected to a high potential and the n-side of the junction diode is connected to a low potential, the junction diode is said to be in forward bias.
When voltage is applied across the p-n junction diode, on the p-side at the junction boundary, electrons from the adjacent depletion layer (negative ion layer) attracted and move towards the positive terminal of the battery and leave behind holes, creating a new hole layer. Consequently, the width of this negative ion layer is reduced. Similarly, on the n-side, holes from the adjacent depletion layer (positive ion layer) move towards the negative terminal of the battery, creating a new electron layer. Consequently, the width of this positive ion layer is reduced. Thus, the thickness of the depletion layer is reduced. The depletion layer offers resistance (acts as a barrier) to the flow of electrons and holes across it.
The applied voltage (V) and barrier potential (VB) are in the opposite direction in forward bias, the barrier height is reduced, and the effective barrier height in forward bias is (VB – V).
Under the influence of the applied voltage, electrons from the n-side repel to the p-side (where they are minority carries) and holes from the p-side cross the junction and reach the n-side (where they are minority carries). This process is known as minority carrier injection.
As we increase applied voltage, current across the junction diode starts increasing exponentially as there is less obstruction (less resistance offered by depletion layer) in movement of electrons and holes, and this current is known as forward current.
The forward voltage at which current across the junction diode starts increasing exponentially is called the knee voltage or cut-in voltage.
Important questions from topic
What is knee voltage?
The forward voltage at which current across the junction diode starts increasing exponentially is called the knee voltage or cut-in voltage.