Schottky Diode
A metal-semiconductor diode having high speed of switching and very low forward biasing voltage drop is known as Schottky diode. The symbol used for Schottky diode is as:
Construction of Schottky Diode
A Schottky diode is made up by overlapping a metal such as gold, silver, tungsten or aluminium over an n-type semiconductor and form a metal-semiconductor junction:
Metal side of the Schottky diode is used as anode and the other side with semi-condor is used as cathode. Both the metal and n-type semiconductor have electrons as majority charge carriers, and there are very fewer holes present in the metal. In forward biasing, the majority charge carries moved very rapidly in the metal region and has more kinetic energy. So, a Schottky diode is also called a hot barrier diode.
Working of Schottky Diode
In forward biasing, the majority charge carriers’ electrons move very rapidly from n-region to the metallic region. As compared to the electrons in the metallic region, the electrons in the n-region have high kinetic energy, and they are also called hot carriers.
Before conduction in the forward biasing, there is a voltage drop in a diode. This voltage drop in normal PN-junction is between 0.6V to 1.7V. But for a Schottky diode this voltage drop is between 0.15V to 0.45V, which make it more useful than the other diodes.
Similarly, on switching from forward to reverse biasing a normal PN-junction diode, the current does not stop quickly as there are some electrons present in the junction and do not recombine with the holes and produce a charge in it. Due to this charge, the diode takes some time in switching from forward to reverse biasing.
In a Schottky diode, only electrons as majority charge carriers are responsible for the flow of current in forward biasing. Due to heavy movement of majority charge carriers from n-region to the metallic region, the junction near to the n-region contains no charge carriers and acts as surface region for more conduction of electrons.
There are no holes as minority charge carriers and therefore, there is no depletion region formed. So, there is no charge stored in the junction on switching from forward to reverse biasing and current stops very fast as compared to other diodes.
IV-Characteristics of Schottky Diode
Voltage drops in forward biasing as very in Schottky diodes. The forward voltage drop in Schottky diode is between 0.15V to 0.45V. The voltage drops increases as the current through the diode increase, so Schottky diodes are used in low current applications. On comparing with simple PN-junction, IV characteristics of a Schottky diode are steeper.
Applications of Schottky Diode
Schottky diodes are used in designing rectifier circuits. As it has high current density and low
Schottky diodes are used in transistor clamping circuits as switching diode. It is connected between the driver transistor and the collector. The Schottky diode provides high current density with low voltage loss when it is turned on. In switching off, the Schottky diode provides less recovery time in reverse biasing.
In solar cell, Schottky diodes are used to protect the flow of reverse current. Very low voltage drop make it energy efficient in solar cells.
Conclusion
A metal-semiconductor diode having high speed of switching and very low forward biasing voltage drop is known as Schottky diode. It is made up by joining a metal and an n-type semiconductor. On both sides of the junction, the majority charge carriers are electron and very fewer holes are present in the metal side.
