Forward bias and Reverse bias

An external voltage is placed across the PN-junction diode during forward biassing. This voltage removes the potential barrier and creates a low-resistance route for current passage. The positive portion of the device is connected to the supply’s p-terminal, while the negative region is connected to the device’s n-type. Because the potential barrier voltage is so low (almost 0.7 V for silicon and 0.3 V for germanium), only a little amount of electricity is necessary to completely remove the barrier. The complete removal of the barrier results in a low resistance channel for current flow. As a result, current begins to flow across the connection. Forward current is the name for this type of current. The negative part of the battery is linked to the positive terminal, while the positive region is connected to the negative terminal in reversed bias. The potential barrier’s strength is increased by the reverse potential. The charge carrier flow across the junction is obstructed by the potential barrier. It produces a high-resistance route through which no current can pass. 

Forward Biased PN junction

When the p-type area of a PN junction is linked to the positive terminal of a voltage source and the n-type region is connected to the voltage source’s negative terminal, the junction is said to be forward-biased. Electrons that participated in covalent bond production in the p-type material will be attracted towards the terminal in this forward-biased situation due to the attraction of the positive terminal of the source. As a result, covalent connections are destroyed and electrons are transferred to the positive terminal. As a result, the concentration of electrons in the crystal near the terminal rises, and these electrons recombine with holes here. The electrons of negative ions come out and recombine with those holes, creating additional holes in the layer, due to the increased concentration of holes near to the negative impurity ions layer. As a result, the width of the negative ions layer decreases, and the layer eventually evaporates. Similarly, because of the source’s negative terminal, free electrons in the n-type area will flow towards the junction, where they will encounter a layer of positive impurity ions, recombine with these ions, and form free electrons within the layer. As a result, the width of positive impurity ions shrinks and eventually vanishes. Both layers of ions will vanish in this manner, and there will be no more depletion layer. Free electrons from the n-type region can easily migrate to the p-type region, and holes from the p-type region to the n-type region in the crystal once the depletion layer has vanished. As a result, there should be no barrier to current flow, and the PN junction should act as a short circuit. 

Reverse Biased PN junction

When a voltage source’s positive terminal is connected to the n-type area and its negative terminal is connected to the p-type region. The PN junction is considered to be reverse biased when it is in this state. The potential created across the p n junction when no voltage is applied is 0.3 volts at 25oC for germanium on the junction and 0.7 volts at 25oC for silicon p n junction. The polarity of this potential barrier is identical to the polarity of the voltage source used in the reverse biased situation. The barrier potential created across the PN junction increases when the reverse biased voltage across the PN junction is increased. As a result, the PN junction has been expanded. When the source’s positive terminal is connected to the n-type area, the free electrons in that region are attracted to the source’s positive terminal, resulting in the formation of more positive impurity ions in the depletion layer, thickening the layer of positive impurity ions. Since the source’s negative terminal is connected to the p-type region of the junction, electrons are injected into this region at the same time. The electrons move towards the junction due to the positive potential of the n-type area, combining with holes next to the layer of positive impurity ions to form more positive impurity ions in the layer. As a result, the layer’s thickness grows. As a result, the depletion layer’s total width grows, as does its barrier potential. The depletion layer’s width will continue to increase until the barrier potential meets the reverse biased voltage applied. Although this increase in barrier potential will continue up to the supplied reverse-biased voltage, the depletion layer will disappear due to Zener and avalanche breakdowns if the applied reverse-biased voltage is sufficiently high. It’s also worth noting that after the reverse biased depletion layer is completed, charge carriers (electrons and holes) no longer drift through the junction since the potential barrier opposes the applied voltage, which is the same as the potential barrier. Minority carriers, which are thermally produced electrons in a p-type semiconductor and holes in an n-type semiconductor, cause a small current to pass from the n-type to the p-type area. 

Conclusion

A rectifier diode is a device that is used to rectify alternating electricity. One of the components of high-frequency electronics is the Gunn diode. In electronic systems, the Zener diode is used to stabilise current and voltage. A photodiode is a type of photodetector. A switching diode is a device that is used to switch between two states quickly. A tunnel diode is a type of diode that is employed in the negative dynamic resistance section of the circuit. The infrared light spectrum is emitted by LEDs. When a voltage is applied in reverse biased condition, a variable capacitance diode is