Reverse biased generally refers to how a diode is employed in a circuit. If a diode is reverse biased, the voltage at the cathode is gets higher than that at the anode. Hence, no current will flow till diode breaks down. Connecting the P-type region to the negative terminal of the battery and the N-type region to the positive terminal corresponds to reverse bias. The connections are demonstrates in the following diagram:
Figure: (a) Blocks of P and N semiconductor in contact have no exploitable properties. (b) Single crystal doped with P and N type impurities develops a potential barrier.
This type of separation of charges at the PN junction constitutes a potential barrier. This potential barrier has to be overcome through an external voltage source to form the junction conduct.
Figure: A silicon p-n junction in reverse bias.
The creation of the junction and potential barrier occurs during the manufacturing process. The magnitude of the potential barrier is a function of the materials employed in manufacturing. Silicon PN junctions comprises a higher potential barrier than germanium junctions.