In case of p−n junction diode, when it is reverse biased, the reverse voltage supports the barrier potential and hence the width of the depletion layer increases.
In forward biasing, the width decreases as the forward voltage opposes the potential barrier. The width of the depletion region increases, if the diode is further doped heavily as the movement of charge carrier decreases.
Also, when the p - n junction is light doped, the width of depletion region increases, due to increase in the potential barrier: