Mumbai University > EXTC > Sem 3 > Analog Electronics 1

Marks: 5 M

Year: Nov 2013

1. Construction:

• In schottky diode a metal-semiconductor junction is formed.
• Normally semiconductor material used is n-type silicon (sometimes p-type silicon is also used) and the metals used are aluminum, molybdenum, platinum, chromium or tungsten, and certain silicides, e.g. palladium silicide and platinum silicide
• The metal side acts as the anode and n-type semiconductor acts as the cathode of the diode.
• Choice of metal and semiconductor determines different set of characteristics for device such as increased frequency range, lower forward bias.
• Due to sharp edges of schottky diode high electric field is produced at the edges which cause breakdown effect. To overcome these problem various technique are used these are guard ring and overlap of metalized area.

Fig1 Cross sectional view of schottky diode.

2. Operation:

• 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 PN junction diode in both forward and reverse bias region. Thus when we apply same voltage in forward bias and reverse bias to schottky and pn junction diode we get higher current from schottky diode. The effect is desirable in forward bias but undesirable in reverse bias.