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

voltage

Voltage, is is the difference in potential between two points  in an electric field. also called electromotive force. voltage is the   pressure from an electrical circuit’s power source that pushes charged electrons (current).           grater the voltage grater the flow of electric current. Voltage is symbolized by   V or E . The standard unit is the volt. One volt will drive one columb  (6.24 x 10 18 ) charge.such as electronics through a resistance of one ohm. Voltage can be direct or alternating. A direct voltage maintains the same polarity. In an alternating voltage, the polarity reverses direction periodically. The number of complete cycles per second is the frequency which is measured in hertz.
3 comments
Read more

BJT (bipolar junction transistor)

A bipolar junction transistor is a three terminal semiconductor current controlled device with two P-N junctions. The three terminals are emitter(E), base(B) and collector(C). the emitter junction is heavily doped, base is less doped and made very thin and collector terminal is moderately doped. Collector has grater size than emitter and base terminal is thinner than both. (The thinner the base, the stronger the E-C electric field, and the larger the impact of a small current injected into the base. Explained clearly in active mode operation below) emitter terminal is moderate in size. A BJT has two types of transistors: NPN transistor PNP transistor NPN transistor : In an NPN transistor a p-type material is sandwiched between two n-type materials. [gallery ids="979,978" type="rectangular"] PNP transistor : In a PNP transistor a n-type material is sandwiched between two p-type materials. [gallery ids="989,990" type="rectangular"] Oper...
2 comments
Read more

resistor & potentiometer

Resistor is a two terminal passive electrical component that implants electrical resistance. in electronic circuits, resistors are used to reduce current flow. ohm's law : The behavior of an ideal resistor is dictated by the relationship specified by ohm's law. Ohm's law states that the voltage (V) across a resistor is proportional to the current (I), where the constant of proportionality is the resistance (R). resistors in series & parallel : The total resistance of resistors connected in series is the sum of their individual resistance values. The total resistance of resistors connected in parallel is the reciprocal of the sum of the reciprocals of the individual resistors. resistor color code : 1 potentiometer :  it is three terminal variable resistor.
1 comment
Read more