The process of applying a potential difference across a p-n junction diode to get it ready for its operation is called biasing of p-n junction diode. There are two types of biasing circuit. They are:
- Forward biasing
- Reverse biasing
A p-n junction diode is said to be forward biased if its p-type is connected to positive terminal of battery and n-type is connected to negative terminal of the battery.
In case of forward biasing, the positive charge of battery repels the hole of p-side of the diode and negative charge of battery repels the electrons of n-side of the diode. Due to this reason, the depletion layer at the junction of the diode decreases and the forward resistance of diode also decreases. Hence the current conduction will be easier in the diode due to current conduction by majority charge carriers. Electrons in the n-region and holes in the p-region are majority charge carriers. In p-n junction diode,
- width of the depletion layer decreases.
- the junction offers very low resistance called as forward resistance.
- potential barrier is reduced and it is eliminated at some forward voltage (0.3 to 0.7 V).
- the current passing through the diode is due to majority charge carrier.
A p-n junction diode is said to be reverse biased if its p-type is connected to negative terminal of battery and n-type is connected to positive terminal of the battery.
In the reverse biasing of p-n junction diode, the electrons from the n-region are attracted towards the positive terminal of the battery and holes form the p-region are attracted towards the negative terminal of the battery. Due to this reason, the depletion layer of a diode increases and the diode offers very high resistance. This resistance offered by a p-n junction diode during its reverse biasing is called reverse resistance.
In the reverse bias, very small amount of charge flows through the diode due to minority charge carriers. Electrons of p-region and holes of n-region are minority charge carriers. These minority charge carriers are pushed towards the junction where they recombine and allow electrons to enter and leave the p-n junction diode. This movement of very low number of electrons constitutes a current known as reverse current. This reverse current is very low in comparison to the forward current. In reverse biasing of p-n junction diode,
- Diode offers very high resistance called reverse resistance.
- The depletion layer increases.
- Current conduction is due to minority charge carriers.
- The barrier potential increases significantly.