Mode of operations of PN-Junction Diode:

1. Forward Bias:- In this mode P side is connected to positive terminal of battery and n side is connected to negative terminal to battery. In forward bias diffusion current is more than drift current. Due to forward bias connection, the height of the potential barrier decreases and the width of the depletion region is also reduced. In forward bias current flows due to flow of majority charge carrier.
2. Reverse Bias:- In this mode P side is connected to the negative terminal of battery whereas N side is connected to positive terminal of battery. In reverse bias diffusion current is less then drift current. The height of potential barrier increases and the width of the depletion region is also increased. In reverse bias current flows due to flow of minority charge carriers.

Dynamic Resistance

R = ΔV/ Δi

Where a ΔV denotes a small change in the in the applied potential difference and Δi denotes corresponding small change in current.

Dynamic resistance is equal to the reciprocal of the slope of the i – V characteristic.

Types of Break Down of Diode

1. Avalanche Breakdown: The holes in the n side and the conduction electron in the p side are accelerated due to the reverse-bias voltage. If this minority charge carrier acquires sufficient Kinetic energy from the electric field and collides with a valence electron, the bond will be broken and the valence electron will go into the conduction band. Thus a hole-electron pair will be created. Breakdown occurring in this manner is called avalanche breakdown.
2. Zener breakdown: Break down may also be done by direct breaking of valence bonds due to high electric field. When breakdown occurs in this manner is called zener breakdown.