State briefly the processes involved in the formation of a p-n junction explaining clearly how the depletion region is formed. Using the necessary circuit diagram, show how the V-I characteristics of a p-n junction are obtained in (i) Forward biasing (ii) Reverse biasing. How are these characteristics made use of in rectification?

(a) When an electron diffuses from n to p due to the difference in charge carriers of the two regions of a p-n junction, it leaves behind a positive charge (ionized donor) on the n-side which is immobile as it is bonded by surrounding atoms. Thus, a layer of positive and negative charges develops on the n-side and p-side of the junction respectively. Hence, a space charge region is formed on both sides of the junction which is called the depletion layer or depletion region. (b) (i) In Forward bias, the p-side of the diode is connected to the positive terminal of the battery and the n-side of the diode is connected to the negative terminal of the battery. The applied voltage is slowly increased, and the current in the circuit is measured and plotted. It is observed that beyond the knee voltage, the current rises rapidly. (ii) In reverse bias, the n-side of the diode is connected to the positive terminal of the battery and the p-side to the negative terminal. The applied voltage is slowly increased, and it is observed that almost no current flows in the circuit until a substantial reverse breakdown voltage. Beyond this point, the current rises suddenly, and the diode works in the reverse breakdown region. A diode, hence, passes only positive values of voltage and blocks negative values of voltage. When applied across an AC source, it passes the positive cycles and blocks the negative cycles. Hence, it is used for rectification purposes.