Semiconductor Electronic: Material, Devices And Simple Circuits — Physics STD 12 Science — Question

Diodes of this type are formed during the crystal pulling process. $P$ and $N-$type impurities can be alternately added to the molten semiconductor material in the crucible, which results in a $P-N$ junction when crystal is pulled. After slicing, the larger area device can then be cut into a large number of smaller$-$area semiconductor diodes. Though such diodes, because of larger area, are capable of handling large currents but larger area also introduces more capacitive effects, which are undesirable. Such diodes are used for low frequencies.
Alloy Type or Fused Junction Diode: Such a diode is formed by first placing a $P-$ type impurity $($a tiny pellet of aluminium or some other $P-$ type impurity$)$ into the surface of an $N-$type crystal and heating the two until liquefaction occurs where the two materials meet. An alloy will result that on cooling will give a $P-N$ junction at the boundary of the alloy substrate. Similarly, an $N-$type impurity may be placed into the surface of a $P-$ type crystal and the two are heated until liquefaction occurs. Alloy type diodes have a high current rating and large $\text{PIV} ($peak inverse voltage$)$ rating. The junction capacitance is also large, due to the large junction area.