Basics of electronics- P-N Junction Diode

Introduction

A P-N junction diode acts as the fundamental unit in every part of electronics. To clear your concepts on this topic, go through the following article. We have taken a step-by-step approach to help you gain expertise in solving the problems based on the p-n junction diode. We initially begin with explaining the meaning of the p-n junction diode, its formation, characteristics, and the various types. After that, we will understand its significance in power electronics devices.

The FAQ section at the end will answer all your doubts related to this topic. So, let us begin with our guide to the p-n junction diode!

What is a p-n junction diode?

A p-n junction diode is a combination of two layers of semiconductors, one p-type semiconductor and another n-type semiconductor. These two layers, when placed together, form a p-n junction between themselves and hence the name comes as p-n junction diode. Its special feature lies in its ability to regulate current as a switch. The diode has two terminals, namely anode and cathode. The p-side of the diode forms the anode and the n-side forms the cathode.

The p-n junction diode behaves differently based on the bias it is subjected to. In the field of electronics, bias refers to the fashion in which voltage is applied across the anode and cathode terminal of the diode. There are two types of bias- forward bias and reverse bias. Characteristics of a p-n junction in both the bias conditions are explained ahead.

In the field of electronics, from a diode to a transistor, the regulation or conduction of current takes place via the formation of this p-n junction only. This is why it finds use in many parts and products that use electronics components in India or abroad.

Formation of p-n junction diode

The p-layer of the p-n junction diode is rich in holes or positive ions, whereas the n-layer has a dominant number of electrons or negative ions. Under normal conditions with no bias applied, the excess holes from the p-region and excess electrons from the n-region migrate towards the point of contact of p-layer and n-layer. These charge carriers, after coming together, form a no-charge region called the depletion layer. The depletion layer is what specifically gives rise to a ‘p-n junction’.

After the p-n junction is formed, there exists a barrier potential/voltage that prohibits other charge carriers from moving in either direction. To have successful conduction across the diode, the bias applied across the diode must overcome this barrier potential. The value of barrier potential is different for different types of diode. It is 0.7 V for Silicon diode and 0.3 V for germanium diode.

P-N junction diode in forward bias

Forward bias refers to the configuration of applied voltage in which the anode terminal of the diode is at a higher potential than the cathode terminal. Thus, we can say that a forward-biased p-n junction diode has anode and cathode terminals connected to positive and negative terminals of a battery.

Since the anode terminal or p-layer of the diode is connected to the positive terminal of the battery, the dominant holes in the p-region experience a repulsive force towards the junction. The electrons in the n-region experience a repulsive force due to the negative terminal of the battery.

In this movement of the charge carrier, some charge carriers get diffused into the space-charge region of the depletion layer while others cross the junction and move towards the other terminal of the battery. As a result, the depletion layer width in a forward-biased p-n junction diode decreases. Due to less depletion width, charge carriers find it easy to move across the junction resulting in proper conduction.

Therefore, the p-n junction diode conducts forward diode and also acts as a closed switch.

P-N junction diode in reverse bias

A reverse-biased diode has anode and cathode terminals connected to the negative and positive terminals of the battery, respectively. In this configuration, the charge carriers of either side of the p-n junction move away from the junction, and hence the depletion layer width increases.

Due to increased depletion layer width, the potential barrier increases. It approximately blocks the passage of movement for charge carriers. As a result, the p-n junction diode acts as an open switch in reverse bias conditions. However, a magnitude of few microamperes still flows across the diode.

Therefore, whenever there is a need for an open switch in electronics, the p-n junction diode is used in reverse bias.

P-N junction diode examples

Some widely used examples of p-n junction diodes used in the field of power electronics:-

•       Photodiode
•       Schottky Diode
•       Zener Diode
•       Solar Photovoltaic cells

These devices are significantly used by electronics companies in India to manufacture many gadgets.

 Conclusion

P-N junction diodes are the essential components of the electronics segment of engineering. From a small electronic watch to a fully-fledged computer, p-n junction diodes are used everywhere. One of the most common applications of a p-n junction diode, i.e. as a switch, is described above.

The forward and reverse bias characteristics have also been explained. Additionally, a list of examples of electronics components is listed above that make use of the p-n junction diode. We hope you have a good understanding and a better grasp of this topic.