Question

Explain how a potential barrier is developed in a p-n junction diode.

Answer 1

During the formation of p-n junction, and due to the concentration gradient across p-, and n- sides, holes
diffuse from p-side to n-side (p → n) and electrons diffuse from n-side to p-side (n → p). This motion of  charge carries gives rise to diffusion current across the junction. When an electron diffuses from n → p, it leaves behind an ionised donor on n-side. This ionised donor (positive charge) is immobile as it is bonded to  the surrounding atoms. As the electrons continue to diffuse from n → p, a layer of positive charge (or positive space-charge region) on n-side of the junction is developed.

Answer 2

In a p-n junction diode, holes are the majority carriers on the p side whereas electrons are the majority carriers on the n-side of the semiconductor. Due to the diffusion of majority carriers from p-region to n-region, the p-region becomes less positive and n-region becomes less negative. An imaginary voltage is developed across the junction which prevents further movement of majority carriers across the junction. The voltage so developed is known as the potential barrier.