When a p-n junction diode is subjected to reverse biasing :

When a p-n junction diode is reverse biased, a negative voltage is applied to the p-side and a positive voltage to the n-side, causing the depletion region to widen and the barrier potential to increase. This creates a high resistance that prevents the flow of majority carriers, so only a very small current (reverse saturation current) due to minority carriers flows, making the diode act as an open switch.