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Avalanche diode
In electronics, an avalanche diode is a diode (made from silicon or other semiconductor) that is designed to experience avalanche breakdown at a specified reverse bias voltage. The junction of an avalanche diode is designed to prevent current concentration and resulting hot spots, so that the diode is undamaged by the breakdown. The avalanche breakdown is due to minority carriers accelerated enough to create ionization in the crystal lattice, producing more carriers which in turn create more ionization. Because the avalanche breakdown is uniform across the whole junction, the breakdown voltage is more nearly constant with changing current compared to a non-avalanche diode.〔L. W. Turner, (ed.), ''Electronics Engineer's Reference Book, 4th Edition'', Newnes, 1976 pages 8-9 to 8-10〕
The Zener diode exhibits an apparently similar effect in addition to Zener breakdown. Both effects are actually present in any such diode, but one usually dominates the other. Avalanche diodes are optimized for avalanche effect so they exhibit small but significant voltage drop under breakdown conditions, unlike Zener diodes that always maintain a voltage higher than breakdown. This feature provides better surge protection than simple Zener diode and acts more like a gas discharge tube replacement. Avalanche diodes have a small positive temperature coefficient of voltage, where diodes relying on the Zener effect have a negative temperature coefficient.〔Jacob Millman ''Microelectronics'', McGraw-Hill, 1979 ISBN 0-07-042327-X, pp. 45-47〕
==Uses==
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