Reverse and forward bias

Reverse bias: A diode is said to be reversed biased if the p-region is connected to the negative terminal and n-region is connected to positive terminal of the battery. In a reversed biased diode, the depletion region of the n-type material will increase due to the large number of free electrons drawn to the positive potential of the applied voltage. Similarly, the number of uncovered negative ions in the p-type material will increase. Due to this, the depletion region widens establishing a great barrier across the junction. The majority carriers cannot overcome the potential barrier resulting in no flow of current. However, the minority carriers can flow across the junction resulting in a flow of current even in reverse-bias conditions, known as reverse saturation current.

Forward bias: A diode is said to be forward biased if the positive terminal and n-region is connected to the negative terminal of the battery. When a diode is forward biased, the electrons in the p-type material will recombine with the ions near the boundary and hence reduce the width of the region results in a heavy majority flow across the junction. An electron of the n-type material has a strong attraction for the positive potential applied to the p-type material. Similar is the case for the holes present in p-type material. As the applied bias increases in magnitude, the depletion region will continue to decrease in width until, a flow of electrons can pass through the junction resulting in an exponential rise in current.