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schottky diode

introduction:


schottky diode is named after named after German physicist Walter H. Schottky. it is also called as hot carrier diode or surface barrier diode.




[caption id="attachment_729" align="aligncenter" width="289"]800px-schottky_diode_symbol-svg symbol of schottky diode[/caption]

construction :


In P-N junction diode semiconductor(P-type)-semiconductor(N-type) junction is formed but, in the case of schottky diode metal-semiconductor junction is formed. basically metals used are molybdenum, platinum, chromium, tungsten Aluminium, gold e.t.c and the semiconductor used is N type silicon is used.


schottk_const



working :



  • Schottky diode is often referred as “majority carrier diode”..

  • When materials are joined, electrons in n-type silicon immediately flow into metal because the electrons in semi conductor are at higher energy level than metal and hence electron flow is established. The flow of electrons stops when Fermi level of two materials are at same level.

  • Due to flow of electrons into metal from semiconductor, metal develops negative charge while semiconductor develops positive charge this give rise to depletion region at the boundary of two materials and corresponding voltage is known as built-in potential.

  • On the application of a forward bias greater than the built-in-potential the current starts to flow through the diode.

  • The width of the barrier in schottky is less than that of normal P-N junction diode in both forward and reverse bias region. Thus when we apply same voltage in forward bias and reverse bias to schottky and P-N junction diode we get higher current from schottky diode. The effect is desirable in forward bias but undesirable in reverse bias because of high leakage current.


Advantages over P-N junction diode:


Low turn on voltage : 


The turn on voltage for the diode is between 0.2 and 0.3 volts for a silicon diode against 0.6 to 0.7 volts for a standard silicon diode. This makes it have very much the same turn on voltage as a germanium diode.


NOTE :  as forward voltage drop is very low power dissipation is also very low then temperature at junction also reduces.


analysis (approx):  consider a P-N junction diode with vf  is 0.7 V and assume 500mA are flowing through it then power 350 mW then temperature at junction is given as 51oc. but, in the case of schottky diode  vf  is 0.345 V assume same 500mA flowing through it then power = 173mW. then junction temperature is given as 38.2oc.


Fast recovery time:  

The fast recovery time because of the small amount of stored charge means that it can be used for high speed switching applications.


   schott


NOTE :

In every cycle P-N junction diode takes lot of time allowing the current to flow back.

Low junction capacitance:

In view of the very small active area, often as a result of using a wire point contact onto the silicon, the capacitance levels are very small.



characteristic curves :


Schottky-Characteristic.png

schottkycurve

 

 
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