Circuit diagrams of $p n$ junction under forward bias and reverse bias Explanation of $p - n$ junction working for forward and reverse bias Characteristic curves for the two cases In forward bias, applied voltage does not support potential barrier. As a result, the depletion layer width decreases and barrier height is reduced. Due to the applied voltage, electrons from $n$ side cross the depletion region and reach $p$ side. Similarly holes from $p$ side cross the junction and reach the $n$ side. The motion of charged carriers, on either side, give rise to current. $\frac{1}{2}$ In reverse bias, applied voltage support potential barrier. As a result, barrier height is increased, depletion layer widens. This suppresses the flow of electrons from $n \rightarrow p$ and holes from $p \rightarrow n$. Diffusion current decreases. The electric field direction of the junction is such that if electrons on $p$ side or holes on $n$ side in their random motion comes close to the junction, they will be swept to its majority zone. This drift of carriers give rise to the current called reverse current.