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Revision as of 09:20, 4 January 2006
The Schottky diode (named after German physicist Walter H. Schottky) is a semiconductor diode with a low forward voltage drop and a very fast switching action. A typical application is discharge-protection for solar cells connected to lead-acid batteries. While standard silicon diodes have a forward voltage drop of about 0.6 volts, Schottky diodes have a drop of only about 0.3 volts. This is due to the higher current density in the Schottky diode.
A Schottky diode uses a metal-semiconductor junction as a Schottky barrier (instead of a semiconductor-semiconductor junction as in conventional diodes). This Schottky barrier results in both very fast switching times and low forward voltage drop.
It is often said that the Schottky diode is a "majority carrier" semiconductor device. This means that if the semiconductor body is doped N-type, only the N-type carriers (mobile electrons) play a significant role in normal operation of the device. No slow, random recombination of N- and P- type carriers is involved, so this diode can cease conduction faster than an ordinary PN rectifier diode. This property in turn allows a smaller device area, which also makes for a faster transition. Therefore broad-area Schottky diodes are useful in switch-mode power converters which operate at frequencies approaching 1 MHz. Small-area Schottky diodes are the heart of RF detectors and mixers, which often operate up to 5 GHz.
The most evident limitation of the Schottky diode is difficulty reaching high reverse-bias voltage ratings, and relatively high series resistance when high voltage ratings are attempted. Relatively high reverse leakage current may present an issue in some applications.
Commonly encountered Schottky diodes include the 1N5817, and Schottky metal-semiconductor junctions are featured in 7400 series logic devices because of their higher switching speeds and lower voltage drops.