The potential barrier in p-n junction diode is due to

When a p-n junction is formed, majority charge carriers diffuse across the junction due to the concentration gradient. Electrons from the n-region diffuse into the p-region, leaving behind immobile positively charged donor ions. Similarly, holes from the p-region diffuse into the n-region, leaving behind immobile negatively charged acceptor ions.

These immobile positive and negative ions accumulate near the junction, creating a region devoid of mobile charge carriers known as the depletion region.

The accumulation of positive charges on the n-side and negative charges on the p-side sets up an electric field directed from the n-side to the p-side. This electric field creates a potential difference across the junction, which acts as a barrier to further diffusion of charge carriers. This is known as the potential barrier.

Therefore, the potential barrier is due to the accumulation of positive and negative charges near the junction.

Answer: accumulation of positive and negative charges near the junction.