As the P-N junction starts, due to the concentration gradient across P-and N-sides, holes diffuse form P-side to N side (P →N) and electrons diffuse form N-side to P-side (N → P). This motion of charge gives rise to diffusion current across the junction. As the holes continue to diffuse,a layer of negative charge (or negative space-charge region) on the P-side of the junction is developed. This space-charge region of either side of the junction together is known as depletion region.
The loss of electrons for the N-region and the gain of electron by the P-region causes a difference of potential across the junction of two regions. The polarity of this potential is such as to oppose further flow of carriers so that a condition of equilibrium exists. This potential is known as potential barrier.
