Diodes

Semiconductor diodes can use two basic forms of construction, point-contact or junction. Point-contact diodes are still available and used for small-signal purposes where a low value of capacitance between the terminals is of primary importance their main use has been for RF demodulation, but even in this use they are now seldom encountered because the diode action is usually incorporated as part of an IC that combines several functions (such as IF amplification, demodulation and signal processing). Most of the applications for point-contact diodes can be more usefully carried out by devices such as the BAT85 Schottky diode.

Junction diodes are obtainable with a much greater range of voltage and current applications, and are used for most other purposes. Apart from diodes intended for specialized purposes, such as light-emitting diodes, the fabrication materials are silicon or (less commonly) germanium, with germanium used almost exclusively for point-contact diodes. An ideal diode would form a short circuit for current in one direction (the forward direction) and an open circuit for current in the reverse direction.

Practical diodes have a low forward resistance (whose value is not constant) and a high reverse resistance; and they conduct when the anode voltage is a few hundred millivolts more positive than the cathode voltage. Semiconductor diodes conduct using minority carriers, meaning that the electrons carry current through the P-region and holes carry the current through the N-region.

The diode can be destroyed by excessive forward current, which causes high power dissipation at the...