Explain the I-V characteristics in Forward and Reverse Bias

The components of semiconductor diodes are widely used in electrical appliances such as computers, laptops, phones, etc. These can also be referred to as a pn junction whose p region is connected to one diode and n is connected to another. These diodes made of silicon allow current to flow in them. Also, on the pn junction, a depletion layer forms. It neither has holes nor electrons present in it. It is basically a device that acts as a door to control electric current. Semiconductors are less conductive than pure metallic conductors. Therefore, they can even resist the flow of charges. For this reason, diodes are used in most electronic devices. 

pn Junction 

The pn junction forms a boundary between two semiconductors and contains two sides. One of the sides of the pn junction is p-type, whereas the other side is known as n-type. P side of the pn junction is connected to the anode and consists of holes. At the same time, the n side of the pn junction is connected to the cathode and consists of excess electrons. The cathode is negatively charged, while the anode is positively charged and carries an excess of holes. But at the depletion region of the pn junction, both holes and electrons are absent. Hence, if there is a positive voltage at the anode, charges flow in the circuit and vice versa.

The pn junction can be connected in two different ways: forward bias and reverse bias which allow forward current and reverse current, respectively. Read the full article to learn about forward and reverse bias. 

Forward Bias Diode 

A forward bias diode allows current to flow in one direction. When the p side of the pn junction is connected to the positive terminal of the battery used in the circuit, it is known as forward biasing. On the other hand, in the forward bias diode, n-type is connected to the negative terminal. On applying voltage, the depletion region decreases in forward-biased semiconductor diodes. This electrical potential decreases the barrier height. So, when an electric circuit is in forward biasing, the increase in DC voltage increases the current flowing inside the circuit. This current can be considered as forward current. 

Reverse Bias Diode

In reverse bias diodes, the p side of the pn junction is connected to the negative terminal of the battery used in the circuit, while the n-type is connected to the positive terminal. On applying voltage, the barrier width increases in reverse-biased semiconductor diodes. It can be understood in this way: the direction of electrical potential is similar to that of barrier potential, which means if the voltage is increased, it will sum up the barrier potential. Additionally, the motion of the charge carrier will also decrease because of the barrier. Hence, with increased reverse bias voltage, the current flow slows down; however, reverse current will reach a higher value. It can be referred to as junction breakdown, and the reverse voltage is known as breakdown voltage at this point. 

I-V Characteristics in Forward and Reverse Bias 

I-V characteristics of any diode will form a single characteristic curve. In the graph, observe that forward and reverse voltage are marked on the x-axis or horizontal axis, whereas the forward current along with reverse current is plotted on the y axis or vertical axis. The forward voltage is on the right side, while the reverse voltage is on the left side of the graph. 

Forward Bias I-V Characteristics 

In forward biasing, forward current flows in the circuit. When the forward voltage equals zero, the value of forward current is also 0 mA. There is an increase in the current in forward bias diodes with increase in forward voltage till the point known as knee voltage. Beyond this point, the forward current increases rapidly. 

Reverse Bias I-V Characteristics 

When the reverse current flows, it is caused by the less amount of charge carrier. Therefore, the reverse current remains constant for a large part of the voltage applied across the terminals. At the breakdown voltage level, there is an exponential increase in the current. It can also cause overheating of the device.

Conclusion 

To conclude, both the IV characteristics of forward bias and reverse bias are different. In forward bias, there is an easy path for the flow of current, while in reverse bias, forward current is small. As the depletion layer is thick, there is higher resistance to the flow of current. In general terms, reverse bias diodes prevent charge carriers from moving in the circuit. They have a much higher potential difference to increase the strength of the barrier. The characteristics curve gives an idea about the IV characteristics or relation between the current and voltage of reverse as well as forward bias diodes.