Skip to main content

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

 

 
Labels:

Comments

Post a Comment

Popular posts from this blog

inductor

An inductor is a passive electronic component that stores energy in the form of a magnetic field. In its simplest form, an inductor consists of a wire loop or coil. The inductance is directly proportional to the number of turns in the coil. Inductance also depends on the radius of the coil and on the type of material around which the coil is wound.   The standard unit of inductance is the Henry abbreviated H. This is a large unit. More common units are the micro Henry, abbreviated µH (1 µH =10 -6 H) and the milli Henry, abbreviated mH (1 mH =10 -3 H). Occasionally, the nano Henry (nH) is used (1 nH = 10 -9 H).             inductors in series & parallel : applications : Inductors are used extensively in analog circuits and signal processing. Applications range from the use of large inductors in power supplies, which in conjunction with filter capacitors remove  fluctuations from the direct current output.          
1 comment
Read more

Transistor

Introduction: A transistor is a semiconductor device which is used to amplify the signals as well as in switching circuits. Generally, it consists of three terminals emitter(E), base(B) and collector(C) and two P-N junctions. It is one of the active components. It was invented by John Bardeen, William Shockley and Walter Brattain in 1948, in Bell Telephone Laboratories. Transistors are divided into different types depending on their construction and operation. Transistors are basically classified into two types; they are Bipolar Junction Transistors (BJT) and Field Effect Transistors (FET). The BJTs are again classified into NPN and PNP transistors. The FET transistors are classified into JFET and MOSFET. Junction FET transistors are classified into N-channel JFET and P-channel JFET depending on their function. MOSFET transistors are classified into Depletion mode and Enhancement mode. Again depletion and enhancement mode transistors are classified into N-channel JFET and P-channel. d...
2 comments
Read more