To Draw the IV Characteristic Curve for PN Junction in Forward and Reverse Bias

A PN junction diode is formed by joining the p and the n-type semiconductor with a barrier potential between these two semiconductors.


A diode is said to be forward-biased if the current flows in the forward direction because of this, we often call this current the forward current or I. 


The value of the forward current is dependent on the value of the forward voltage with a direct relationship between these two. This direct relationship is called the IV Characteristics of PN Junction.


IV Characteristics of PN Junction

For a PN Junction diode, there are two operating regions and three biasing conditions for the standard Junction Diode. The IV characteristics of PN Junction diode are as follows:

  1. Zero Bias Condition – A conduction when no external voltage potential is applied to the PN junction diode.

  2. Reverse Bias – The voltage potential is connected to the negative terminal i.e., to the n-type material and positive terminal of the battery to the N-type material across the diode which has the effect of Increasing the PN junction diode’s width or the depletion layers between these two semiconductor materials.

  3. Forward Bias – The voltage potential is connected positive, (+ve terminal), i.e., to the P-type material and negative (- ve terminal) to the N-type material across the diode which has the effect of decreasing the PN junction diodes width, or the depletion layer between the two semiconductors.

Now, let’s discuss the IV characteristics of a PN Junction diode in detail:


Forward Bias and Reverse Bias


Forward Bias

From the above context, we understood that if the current flows in the forward direction, but which direction are we talking about? Well! A forward bias characteristic is in the following manner:


A positive terminal of the battery is connected to the p-type conductor whereas a negative terminal is to the n-type. We all know that on applying the potential to the circuit, the current starts from a negative terminal to the positive, i.e., from n-type to the p-type (a built-in electric field is in the direction opposite to that of the applied electric field).


Forward Bias Diagram

Below is the forward bias circuit diagram:

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From the above forward bias diagram, we notice that on applying the electric field to the forward bias circuit diagram, the holes from the p-type semiconductor combine with electrons in an n-type semiconductor. 


A forward bias characteristic is that it reduces the potential barrier, which creates an easy current flow through the forward bias circuit diagram. Also, on increasing the voltage, the magnitude of a current also rises sharply, the same can be seen in the following graph:

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Reverse Bias

The connection in a reverse biasing is opposite to that of the forward biasing. In this type of connection, a positive terminal is connected to the n-type semiconductor whereas a negative terminal is connected to the p-type semiconductor.


One of the reverse bias characteristics is, there is a small change in the value of current with the voltage rise; however, the reverse current increases with the voltage rise. When there is an increase in the reverse current, the depletion layer or the potential barrier between the two semiconductors also rises.


Reverse Bias Diagram

The reverse bias diagram can be better understood in the following manner:

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The below graph represents how the value of the reverse current rises on increasing the voltage or simply the reverse-bias current-voltage characteristics:

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PN Junction Diode Experiment

The flow of electrons from the n-type semiconductor towards the p-type semiconductor of the PN junction takes place when there is an increase in the voltage. 


Similarly, the flow of holes from the p-type semiconductor towards the n-type of the junction takes place along with the increase in the voltage. 


The PN Junction Diode Experiment results in the concentration gradient between both sides of the terminals. Because of the formation of the concentration gradient, there will be a flow of charge carriers from higher concentration regions to lower concentration ones. This motion of charge carriers inside the PN junction diode is the reason behind the flow of current in the circuit.   


PN Junction Diode Characteristics           

  • Semiconductors contain two types of mobile charge carriers, viz: Holes and Electrons, where holes are positively charged and electrons are negatively charged.

  • We can dope a semiconductor with donor impurities like Antimony (N-type doping), so that it contains mobile charges which are basically electrons.

  • A semiconductor can be doped with acceptor impurities viz: Boron (P-type doping) so that this semiconductor contains mobile charges which are primarily holes.

  • The junction region that has zero charge carriers is known as the depletion region.

  • The junction ( or the depletion region) region has a physical thickness that varies with the applied voltage. The depletion region reduces in a forward bias condition whereas it rises in a reverse-biased condition.

FAQs (Frequently Asked Questions)

Question 1: Write Some Applications of the PN Junction Diode.

Answer: The applications of a PN junction diode are as follows:

  • We can use the p-n junction diode as a photodiode, as this diode is sensitive to the light when the configuration of the diode is changed to reverse-biasing.

  • As a solar cell.

  • When the diode is forward-biased, we can use it in LED lighting applications.

  • We can use the PN junction diode as rectifiers in many electric circuits and as a voltage-controlled oscillator in the device like varactors.

  • We can use it in clipping circuits as wave shaping circuits in computers, radios, radars, etc.

  • In detectors and demodulator circuits.

  • As a switch in digital logic designs.

  • In clamping circuits in a TV receiver.

  • In voltage multiplier circuits.

Question 2: What is a PN Junction Diode? List One Property of a PN Junction Diode.

Answer: A PN Junction Diode is a two-terminal semiconductor device. It is made from a small piece of semiconductor material (usually we use Silicon).

A PN junction diode allows the electric current to flow in one direction while opposes the current flow in another direction.

A junction diode can be used to rectify alternating voltage or an alternating current. The circuit employed for this purpose is a Rectifier. 

Hence, a PN junction diode can be used as a rectifier in a way that an alternating voltage is applied across a junction diode that is connected to a load in a series arrangement.