Briefly describe electron and hole motions in a \(p-n\) junction for forward and reverse biases; then explain how these lead to rectification.

In a p-n junction, an area called the depletion region is formed where the positive and negative ions are located, preventing further movement of electrons and holes. The motion of these charge carriers is responsible for the conduction in the junction. Electrons move from the n-side to the p-side across the junction, while holes move from the p-side to the n-side.

In a p-n junction, a forward bias refers to the condition when the external voltage is applied to a semiconductor diode such that the positive terminal is connected to the p-side of the diode and the negative terminal is connected to the n-side of the diode. In reverse bias, the positive terminal is connected to the n-side and the negative terminal is connected to the p-side.

- Forward bias: When the p-n junction is under forward bias, the external voltage decreases the potential barrier at the junction, allowing electrons and holes to overcome the barrier and move across the junction. Electrons from the n-side move to the p-side, recombining with the holes on the p-side, while holes from the p-side move to the n-side, recombining with the electrons on the n-side. As the charge carriers move across the junction, a current is produced. - Reverse bias: In the reverse bias condition, the external voltage increases the potential barrier at the junction, preventing the charge carriers from moving across the junction. The depletion region widens and the number of charge carriers in it decreases. Since there is minimal motion of electrons and holes, the resulting current is significantly smaller compared to the forward bias situation.

Rectification is the process by which an alternating current (AC) signal is converted to a direct current (DC) signal. The unidirectional flow of current in a p-n junction diode under forward bias allows positive half-cycles to pass through while the almost negligible flow of current under reverse bias blocks the negative half-cycles. This results in the conversion of an alternating current (AC) to a pulsating direct current (DC), which is the primary function of a rectifier.