P-N Junction ‒ Reverse Bias

When we apply an external voltage to the diode as shown our model - with the positive terminal connected to the N-type material and the negative terminal connected to the P-type material - external voltage causes the movement of electrons and holes inside the P-N junction. Also, electrons from a wire connected to a negative terminal are injected into the P-type material. This causes further depletion of holes and it produces a widening of the depletion layer. The same result is on the other side (N zone). The positive terminal pulls electrons from the N-type material. The final effect is that an external voltage connected this way leads to the effect of the barrier voltage opposes the external voltage. Any initial movement of charge due to the external voltage will just increase the barrier voltage. Therefore no current will flow through the diode. A diode with this polarity we call reverse biased.