If we join a section of N-type semiconductor material with a similar section of P-type semiconductor material, we obtain a device known as a PN junction. (The area where the N and P regions meet is appropriately called the junction.) The usual characteristics of this device make it extremely useful in electronics as a diode rectifier. The diode is nothing more than a two-element semiconductor device that makes use of the rectifying properties of a PN junction to convert alternating current into direct current by permitting current flow in only one direction. The schematic symbol of a PN junction diode is shown in the figure below. The vertical bar represents the cathode (N-type material) and the arrow represents the anode (P-type material). For further clarification, a pictorial diagram of a PN junction is also illustrated.