A PN junction diode is a two-terminal semiconductor device that allows electric current to flow in one direction only. It is formed by fusing a p-type semiconductor to an n-type semiconductor, creating a potential barrier voltage across the diode junction. The PN junction diode has an asymmetrical conducting two-terminal device, which is better known as the PN Junction Diode. The diode has an exponential current-voltage (I-V) relationship, and therefore its operation cannot be described by simply using an equation such as Ohm’s law.

When the diode is connected in a zero-bias condition, no external potential energy is applied to the PN junction. However, if the diodes terminals are shorted together, a few holes (majority carriers) in the P-type material with enough energy to overcome the potential barrier will move across the junction against this barrier potential. This is known as the “Forward Current” and is referenced as IF. When the diode is in forward bias condition, the p-type is connected to the positive terminal while the n-type is connected to the negative terminal of the external voltage. When the voltage is 0.7 V for silicone diodes and 0.3 V for germanium diodes, the potential barriers decrease, and there is a flow of current.

The p-n junction diode is a basic semiconductor device that controls the flow of electric current in a circuit. It has a positive (p) side and a negative (n) side created by adding impurities to each side of a silicon semiconductor. The ability to control the flow of current in this way makes the p-n junction diode a simple yet powerful semiconductor device. The diode has multiple uses, including rectification of alternating current to direct current, in the detection of radio signals, and emitting and detecting light.