How PN Junction Diode is formed?

PN junction diodes formed after fusing a p-type semiconductor with an n-type semiconductor which induces a potential barrier voltage across the diode junction, resulting in the junction being in equilibrium. However, if we make an electrical connection to the ends of the N-type and P-type materials and then connect them to a battery source, an additional source of energy will now exist to overcome the potential barrier.The addition of this extra energy causes electrons to freely pass through the depletion region from side to side. The operation of the PN junction with respect to the width of the potential barrier produces a disproportionately conductive double-ended device, known as a PN junction diode.

A PN Junction Diode is one of the simplest semiconductor devices around, and which has the electrical characteristic of passing current through itself in one direction only. However, unlike a resistor, a diode does not behave linearly with respect to the applied voltage. Instead it has an exponential current-voltage (IV) relationship and therefore we cannot describe its operation by simply using an equation such as Ohm’s law.

If a suitable positive voltage (forward bias) is applied between the two ends of the PN junction, it can supply free electrons and holes with the extra energy they require to cross the junction as the width of the depletion layer around the PN junction is decreased. By applying a negative voltage (reverse bias) results in the free charges being pulled away from the junction resulting in the depletion layer width being increased. This has the effect of increasing or decreasing the effective resistance of the junction itself allowing or blocking current to flow through the PN junction diodes.

Then the attenuation layer will widen as reverse voltage application is increasing and narrow as forward voltage application will increase. This is due to the difference in electrical characteristics on both sides of the PN junction, resulting in physical changes. One of the results produces rectification as seen in the static IV (current-voltage) characteristic of the PN junction diodes. Rectification is represented by asymmetric current when the polarity of bias voltage is changed as shown below.

Symbol and Static I-V Characteristics of Junction Diode

But before we can use the PN junction as an actual device or as a rectifier, we must first bias the junction, i.e. connect a voltage across it. On the voltage axis above, "Reverse bias" refers to an external voltage difference that increases the potential barrier. An external voltage that lowers the potential barrier is said to operate in the "Front Differentiation" direction. There are two operating regions and three possible "bias" conditions for a standard junction diode, and these are:

  1. Zero Bias: No external voltage potential is applied to the PN junction diode.
  2. Reverse Bias: The voltage potential is connected negative, (-ve) to the P-type material and positive, (+ve) to the N-type material through the diode which has the effect of increasing the width of PN junction diode.
  3. Forward Bias: The voltage potential is connected positive, (+ve) to the P-type material and negative, (-ve) to the N-type material through the diode which has the effect of decreasing the width of PN junction diode.
Prasun Barua

Prasun Barua is an Engineer (Electrical & Electronic) and Member of the European Energy Centre (EEC). His first published book Green Planet is all about green technologies and science. His other published books are Solar PV System Design and Technology, Electricity from Renewable Energy, Tech Know Solar PV System, C Coding Practice, AI and Robotics Overview, Robotics and Artificial Intelligence, Know How Solar PV System, Know The Product, Solar PV Technology Overview, Home Appliances Overview, Tech Know Solar PV System, C Programming Practice, etc. These books are available at Google Books, Google Play, Amazon and other platforms.


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