Schottky barrier diodes, Physics


The Schottky diodes are a semiconductor diode with a low forward voltage drop and a very fast switching action. The voltage drop at forward biases of around 1ma is in the range 0.15v to 0.45v, which makes them useful in voltage clamping application and prevention of transistor saturation. This is because of high current density. Its areas of applications were first limited to the very frequency range due to its quick response time (especially important in frequency applications). In recent years, however it is appearing more and more in low voltage/high current power supplies and AC to DC converts. Other areas of applications of the device including radar systems, Schottky TTL logic for compounds, mixers and detectors in communication equipment, instrumentations, and analogue to digital converters. A Schottky diode uses a metal semiconductor junction as a Schottky barrier (instead of a semiconductor junction as in conventional diodes). Its construction is pretty dissimilar from the conventional P-N junction. The semiconductor is normally n-type silicon (although p-type silicon is sometimes used), while a host of different metals such as molybolenum, platinum, chrome or tungsten are used. In general, however, Schottky diode construction results in a more uniform junction and of ruggedness. In both materials the electrons is the majority carriers. When the materials are joined, the electron in the N-type silicon semiconductor material immediately flows into the adjoining material, establishing a heavy flow of majority carriers. As the injected carriers have a very elevated kinetic energy level as compare to the electrons of the metal, they are usually called “ hot carriers”, the heavy flow of electrons into the metal generates a region close to the junction surface depleted of carriers in the silicon material much like the depletion region in the P-N junction diode. The additional carriers in the metal set up a “negative wall” in the metal at the margin between the two materials. The net consequence is a surface barrier between the two materials preventing any additional current. That is any electrons in the silicon material face a carrier free region and a “negative wall” at the surface on the metal. The application of forward bias will reduce the strength of the negative barrier through the attraction of the applied positive voltage for electrons from this region. The result is a result to the heavy flow electrons across the boundary, the magnitude of which is controlled by the level of the applied bias potential.

Posted Date: 7/9/2012 2:22:04 AM | Location : United States

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