Schottky Diode: Definition, Working & Characteristics

This diode is mostly used in radio frequency (RF) circuits or in power supplies. So let's get started with the basics of Schottky Diode:

Schottky Diode

• Schottky Diode (also called Schottky Barrier Diode), discovered by German physicist Walter H. Schottky, is a special type of diode in which P-layer (of PN junction) is replaced by the metal layer ( i.e. Aluminium, Tungsten, Molybdenum, Platinum etc.), while the N layer is of silicon (semiconductor - same as in normal diode).

• In a normal diode, PN junction is composed of semiconductor material only (i.e. Silicon or Germanium), while in Schottky diode, PN junction is composed of metal & semiconductor, as shown in the below figure:

• You can see in the above figure, we have a Metal Region instead of P-Type Region, thus its junction is a doping result of metal and semiconductor (Silicon).
• Schottky diode symbol is slightly different than that of normal diode but packaging is the same.
• Forward voltage loss of Schottky diode is 0.15V to 0.45V, which is quite low as compared to normal diode.
• Because of low voltage consumption, its response rate is high and thus used in fast switching applications.
• If we increase the doping of a semiconductor, it will decrease the width of the depletion region.

Schottky Barrier

• The depletion region created after the doping of metal & semiconductor (as in Schottky diode) is called Schottky Barrier.
• In simple words, the Schottky barrier is a minimum Potential Energy required for electrons to cross the barrier.
• Once the P.E. of electrons exceeds a certain limit (depends on doping), they overcome the Schottky barrier and start flowing across the Schottky diode.
• The Schottky barrier's width is quite smaller than the depletion region in a normal diode.
• It normally takes 0.2V to 0.3V to overcome the Schottky Barrier, while for normal depletion regions, it takes 0.6V to 0.7V.
• There are further 2 types of Schottky barrier:
  • Rectifying Schottky barrier.
  • Non-rectifying Schottky barrier.

 Schottky Diode Energy Band

• The potential energy level of electrons outside the material is known as the Vacuum level.
• The amount of energy needed to move electrons from the Fermi level to the vacuum level is known as the work function.
• The value of this energy (work function) is different for metals and semiconductors.
• So the electrons in N-type semiconductors have a larger value of P.E than the electrons in metals.
•  Let's see the diagram of the energy band of Schottky diode:

Schottky diode Characteristics Curve

• Now, let's discuss the voltage and current characteristics of the Schottky diode.
• It has low forward voltage loss that's why its characteristic curve is close to current axes as compared to normal diodes.
• As we discussed earlier, voltage drop in Schottky is about 0.2V to 0.3V but in normal diodes, it's 0.6V to 0.7V.
• When the applied voltage to Schottky diode exceeds this limit, the diode becomes forward biased.
• Schottky Diode has Low Reverse Breakdown Voltage as compared to normal diode and if this limit exceeds, it may damage the component permanently.

Schottky Diode Vs Normal Diode

• In Schottky Diode, number of electrons is quite greater than number of holes and thus electrons are solely responsible for the flow of current, can be termed as Unipolar, while in normal diode, both holes & electrons are equally responsible for the current flow and thus termed as Bipolar.
• In the below figure, you can see the difference between Schottky Diode & normal diode:

Schottky Diode Advantages

• It has a low forward voltage drop.
• It has a fast response time.
• It has a fast recovery time, thus highly efficient.
• It has a high current density and thus can handle high current at low voltages.

Schottky Diode Disadvantages

• It has a high reverse saturation current.

Schottky Diode Applications

• It's used in radio frequency appliances.
• It's used in circuits of Logic Gates.
• It's used in designing rectifiers.
• It's used for controlling reverse current in power supplies.