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 PIV (peak inverse voltage) rating. The junction capacitance is also large, due to the large junction area.