Circuit diagrams of $\mathit{p}\mathit{n}$ junction under forward bias and reverse bias
Explanation of $\mathit{p}-\mathit{n}$ 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 $\mathit{n}$ side cross the depletion region and reach $\mathit{p}$ side. Similarly holes from $\mathit{p}$ side cross the junction and reach the $\mathit{n}$ side. The motion of charged carriers, on either side, give rise to current. $1∕2$ 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 $\mathit{n}\to \mathit{p}$ and holes from $\mathit{p}\to \mathit{n}$. Diffusion current decreases. The electric field direction of the junction is such that if electrons on $\mathit{p}$ side or holes on $\mathit{n}$ 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.