The device in which p-type semiconductor is in contact with n-type semiconductor is known as P-N Junction diode. It is also known as semiconductor diode or simple crystal diode. The P-side refers to anode and n-side refers to cathode. It is represented in the figure below.
Biasing: When diode is connected to an external voltage, it is called biasing. There are two types of biasing.
- Forward biasing
- Backward biasing
1. Forward biasing: When the positive terminal of the battery is connected to p-side and negative terminal is connected to n-side, it is called forward biasing. In this condition, positive terminal on p-side repels the hole while negative terminal on the n-side repels electrons due to which recombination of free electron and hole takes place at the junction which reduced the width of depletion layer and barrier potential. When the applied voltage overcome the barrier potential (VB). a large current flows through the junction and the current is called forward current. The diode offers very low resistance called forward biasing.
In simple words ,when a voltage source is connected to a diode such that the positive side of the voltage source is on the anode and the negative side is on the cathode, the diode becomes a conductor and allows current to flow. Voltage connected to the diode in this direction is called forward bias.
Forward Biased P-N Junction Diode
When a diode is forward biased:
- The width of depletion layer decreases.
- The barrier potential increases.
- The flow of current is due to the majority charge carrier.
- The diode will offer very small resistance called forward resistance.
Reverse biasing: When the negative terminal of the battery is connected to the p-side and positive side is connected to n-side. Then such arrangement is called reverse biasing.In this condition, the negative terminal on the p-side attracts the hole while the positive terminal on n-side attracts the electron due to which majority charge carriers from the majority charge carries from each side are drawn away from the junction. This increases the width of the depletion layer and barrier potential. The applied voltage causes the increase in resistance of the diode which is called the reverse resistance. No current flows due to majority charge carrier.
In simple words, When we reverse the direction of voltage by applying the positive side to the cathode and the negative side to the anode, current doesn’t flow. In effect, the diode becomes an insulator. Voltage connected to the diode in this direction is called reverse bias.
When a diode is reverse biased.
- The width of depletion layer increases.
- The barrier potential decreases.
- There is a flow of negligible current.
- The flow of current is due to the minority charge carrier.
- The diode will offer very high resistance called reverse resistance.