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SCHOTTKY DIODEBY RAMEN GOGOIIMSC 5TH SEM 142017

Contents DiodeSchottky diode

What is a Diode??..

In electronics, a diode is a two terminal electronic component that conducts primarily in one direction

PN diode

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Schottky diodeThe Schottky diode, also known as hot carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal.

A normal silicon diode has a voltage drop between 0.61.7 volts, while a Schottky diode voltage drop is between approximately 0.150.45 volts. This lower voltage drop can provide higher switching speed and better system efficiency.

Schottky Diode Symbol

Things to RememberMistakes about the symbol.

CONSTRUCTIONA metalsemiconductor junction is formed between a metal and a semiconductor, creating a Schottky barrier (instead of a semiconductorsemiconductor junction as in conventional diodes).Typical metals used are molybdenum, platinum, chromium or tungsten; and the semiconductor would typically be N-type silicon.The metal side acts as the anode and N-type semiconductor acts as the cathode of the diode. This Schottky barrier results in both very fast switching and low forward voltage drop.

Schottky Diode

Ohmic ContactIt is a junction between two conductors that has a linear current-voltage(I-V) curve as with Ohms law.

The term ohmic contact implicitly refers to an ohmic contact of a metal to a semiconductor

CONNECTIONS..

mA+-++--

RlViAI

IV CHARACTERISTIC CURVE

Schottky diode I-V characteristicsSchottky diode is a metal-semiconductor (MS) diodeHistorically, Schottky diodes are the oldest diodesMS diode electrostatics and the general shape of the MS diode I-V characteristics are similar to p+n diodes, but the details of current flow are different. Dominant currents in a p+n diodearise from recombination in the depletion layer under small forward bias.arise from hole injection from p+ side under larger forward bias.Dominant currents in a MS Schottky diodesElectron injection from the semiconductor to the metal.

p+n and MS Schottky diodes

p+nMn-Si

Reverse side characteristicsThe reverse leakage current for a Schottky diode is generally much larger than that for a p+n diode.

Since MS Schottky diode is a majority carrier devices, the frequency response of the device is much higher than that ofequivalent p+ n diode.

Reverse recovery timeThe most important difference between the p-n and Schottky diode is reverse recovery time, when the diode switches from conducting to non-conducting state. Where in a p-n diode the reverse recovery time can be in the order of hundreds of nanoseconds and less than 100ns for fast diodes, Schottky diodes do not have a recovery time, as there is nothing to recover from (i.e. no charge carrier depletion region at the junction). The switching time is ~100 ps for the small signal diodes, and up to tens of nanoseconds for special high-capacity power diodes. With p-n junction switching, there is also a reverse recovery current, which in high-power semiconductors brings increased EMI noise. With Schottky diodes switching essentially instantly with only slight capacitive loading, this is much less of a concern.

Advantages

Let see The main advantages

PN Junction Diode

Thermal Image of PN diode

Schottky diode

Thermal Image of Schottky Diode

At lower frequency

At Higher Frequency

Why simple PN diode rectification detoriates??..The is due to charge storage at Junction , the normal diode takes time to turn off, this time is called the reverse recovery time

Why Schottky diode is better??Because of the one side of the junction the Schottky diode has no depletion layer.No depletion layer results in no charge storing in the junction. Therefore no problem in fast switching ON/OFF at higher frequencies.

Disadvantages

Reverse voltage of PN diode

Reverse Voltage of Schottky Diode

LimitationsThe most evident limitations of Schottky diodes are the relatively low reverse voltage ratings for silicon-metal Schottky diodes, typically 50 V and below, and a relatively high reverse leakage current. Some higher-voltage designs are available; 200V is considered a high reverse voltage.Reverse leakage current, because it increases with temperature, leads to a thermal instability issue. This often limits the useful reverse voltage to well below the actual rating.While higher reverse voltages are achievable, they would be accompanied by higher forward voltage drops, comparable to other types; such a Schottky diode would have no advantage

ConclusionSchottky Diodes proves to be a better diode in rectification process at higher frequency and has lower temperature dependence though it has a higher reverse voltage compared to PN Junction Diode.