Page "Diode" Paragraph 27

Normal ( p – n ) diodes, which operate as described above, are usually made of doped silicon or, more rarely, germanium.

Before the development of silicon power rectifier diodes, cuprous oxide and later selenium was used ; its low efficiency gave it a much higher forward voltage drop ( typically 1. 4 to 1. 7 V per " cell ", with multiple cells stacked to increase the peak inverse voltage rating in high voltage rectifiers ), and required a large heat sink ( often an extension of the diode ’ s metal substrate ), much larger than a silicon diode of the same current ratings would require.

The vast majority of all diodes are the p – n diodes found in CMOS integrated circuits, which include two diodes per pin and many other internal diodes.