Tuesday, January 23, 2018

Schottky Diode

       In a schottky diode, unlike a pn-junction diode, a metal  (AL) is directly contacted with semiconductor (n-type) as in left side contact of figure 1(a). The surface barrier so formed is called the Schotkky barrier and the type of contact is a rectifying contact. The AL metal so contacted forms the anode. The cathode is formed by an ohmic contact of Al with n region (heavily doped) below it in the n-type semiconductor; right side of the figure 1(a). At the rectifying contact electrons, the majority carriers, enter in very large numbers (not countable) into the metal surface leaving a small region somewhat  depleted of electrons. There is a heavy concentration of electrons on the metal surface at the interface forming the potential barrier which is lower than in a pn-junction diode,. As a forward bias is applied, conduction takes place by electrons alone; there are no holes on the metal side to move into the semiconductor. The threshold voltage is about 0.3 V compared to that of an ordinary diode which is 0.7 V. Because of electron conduction, switching is very fast in a Schotkky diode as no time is needed for recombination of electrons and holes as in a ordinary diode.

       Schottky diode symbol and its approximate circuit model are given in figure 2(a) and 2(b). The circuit model comprise an ideal diode and a parallel capacitor Cj to account for  junction capacitance.

Chcracteristics of Schottky Diode
       Figure 3 compare the V-I characteristics of a Schottky diode with the ordinary silicon diode. It is seen that
(i)    Cut-in voltage is lower in Schottky diode,
(ii)    The reverse current is greater in the Schottky diode
Fig. 3 V-I characteristics of Schottky diode and Silicon diode

Comparison between Shcottky Diode and Conventional Diode

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