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

relay

A relay is an electrically operated switch. These are remote control electrical switches that are controlled by another switch. A relay is used to isolate one electrical circuit from another. It allows a low current control circuit to make or break an electrically isolated high current circuit path. The basic relay consists of a coil and a set of contacts. The most common relay coil is a length of magnet wire wrapped around a metal core. When voltage is applied to the coil, current passes through the wire and creates a magnetic field. This magnetic field pulls the contacts together and holds them there until the current flow in the coil has stopped. The diagram below shows the parts of a simple relay. Operation: When a current flows through the coil, the resulting magnetic field attracts an armature that is mechanically linked to a moving contact. The movement either makes or breaks a connection with a fixed contact. When the current is switched off, the armature is usually returned by...
1 comment
Read more

P-N junction diode

A P-N junction diode is a basic diode. It is the combination of P-type and N-type semiconductor. symbol : P-N junction and potential barrier : A P-N junction is the basic building block of many semiconductor devices like diodes and transistors. P -n  junctions are formed by joining  n -type and  p -type semiconductor materials. Since the  n -type region has a high electron concentration and the  p -type a high hole concentration this difference in concentration creates density mismatch across junction which results to creation of potential barrier. The value of potential barrier v b  is 0.3 for germanium and 0.7 for silicon. Working : Forward bias: Application of positive charge at p-side pushes holes towards potential barrier and similarly negative charge at N-side pushes electrons towards barrier if input voltage is grater than potential barrier then electrons diffuse from the  n -type side to the p-type side. Similarly, holes flow by diffusion from the p-type side to the n-type side...
4 comments
Read more

resistance & resistivity

Resistance is a measure of the opposition to current flow in an electrical circuit. Resistance is measured in ohms, symbolized by the Greek letter omega (Ω). Ohms are named after George Simon Ohm (1784-1854), a German physicist who studied the relationship between voltage, current and resistance. He is credited for formulating Ohm’s Law. The electrical resistance of a circuit component or device is defined as the ratio of the voltage applied to the electric current which flows through it. The higher the resistance, the lower the current flow and vice-versa. resistivity : The electrical resistance per unit length, area, or volume of a substance is known as resistivity. Table of resistivity Material Resistivity ρ (ohm m) Temperature coefficient α per degree C Conductivity σ x 10 7 /Ωm Ref Silver 1.59 x10 -8 .0038 6.29 3 Copper 1.68 x10 -8 .00386 5.95 3 Copper, annealed 1.72 x10 -8 .00393 5.81 2 Aluminum 2.65 x10 -8 .00429 3.77 1 Tungsten 5.6 x10 -8 .0045 1.79 1 Iron 9.71 x10 -8 .00651...
2 comments
Read more