At a glance
In today’s blog, we will learn about what is Schottky diode how it differs from a normal PN junction diode, its application, and its disadvantage. also, the unique construction also the ohmic contact and rectifying contact and its working.
The following block diagram will help you to undearstand the road map of blog.
Introduction to Schottky diode
The Schottky diode is a semiconductor diode having two terminals formed by diffusing an N-type semiconductor over metal.
The current flow is due to only the majority carriers (electrons); hence, it is a unipolar device.
It is named after the German physicist Walter H. Schottky. This diode is also known as Schottky barrier diode or hot–carrier diode.
The Schottky diode works while connected to forward bias, the same as the PN junction diode. There are three main differences between the PN junction diode and the Schottky diode.
- Low forward drop – for the Schottky diode, it is 0.3 to 0.5, but for the PN junction diode, it is 0.6 to 0.7.
- Dissipates less power and generates less heat
- Reverse recovery time is high (recovery time states how fast the diode responds to switching); also, the switching speed is high.
If we connect the diode to supply and load, it will act as a rectifier while providing current to the load.
If we take the PN junction diode and use it for the above condition, it will rectify the supply and provides voltage for the only positive cycle,
In the negative cycle, it gets reverse biased, but it will conduct for some period in the negative cycle due to low reverse recovery time.
But for the Schottky diode, when we connect it according to the above connections, during the negative cycle, it will get reverse biased and turned off fast, and we get perfect rectification
this is due to the high recovery time of the Schottky diode and its high switching speed .so it will rectify high-frequency signals fast.
Schottky diode – Power Dissipation
Suppose the current passing through PN junction diode, and Schottky diode is 2 amp, and the forward voltage drop for Schottky diode is 0.3 and for PN junction diode 0.7 then power dissipated for both diode will be,
For Schottky diode
The power dissipated = Vf × I
= 0.3 × 2
= 0.6 W
For PN junction diode
The Power dissipated = Vf × I
= 0.7 × 2
= 1.4 W
We can see from the above calculation that the Schottky diode for the same current power dissipation is less than the PN junction diode. And due to which it generates less heat.
Construction
As the above figure shows, it has two regions one is made from the N-type semiconducting material, and the second region is made up of metals such as gold, silver, chrome, platinum, or tungsten. Different material used for construction provides different characteristics of Schottky diode.
N-Type semiconductor part of the diode is constructed from N substrate. To create N – Substrate diffuse p first and then near the contact, we either have P+ or N + at the contact.
The metallic region in the structure acts as an anode while the N-type semiconductor forms a cathode.
The junction created between the metallic region and the N-type semiconductor is the Schottky junction. It provides contact electrodes or metal contact to the semiconductor. It is essential to contact the electrode to a semiconductor device. Therefore this junction is necessary for device characteristics.
The junction created could be rectifying contacts like a standard diode or ohmic contact.
Rectifying contact of Schottky diode
In rectifying the Schottky barrier, the barrier is high enough that there is a depletion region in the semiconductor; near the interface, this gives the barrier a high resistance when small voltage biases are applied to it.
The rectifying contact allows the current to flow in one direction and blocks in another one.
From the characteristics, you can see that rectifying characteristic of the Schottky diode are similar to the PN junction diode, except due to the low forward voltage drop (0.3 – 0.5), it starts conducting earlier.
In this, the diode conducts only in the forward direction; that is, a considerable amount of current flows in a forward direction beyond the forward voltage drop. And opposes the current flow in the reverse direction.
Ohmic contact of Schottky diode
The ohmic contact is a low resistance junction known as non – rectifying contact, provides the current conduction from metal to semiconductor and vice versa.
Theoretically, the current flowing through the diode is equal to the applied voltage. Hence the characteristic of ohmic contact is the linear curve. In this case, the current behavior is the same on either side. Like a resistor, we all know that we can connect the resistor to supply in both directions. There is no polarity to the resistor, so its behavior is linear. The same thing happens during the ohmic contact of the junction.
The characteristics appeared to be a cross-line passing through the origin. In this condition, the diode provides the exact nature of the curve during forward biasing and reverse biasing.
Working of Schottky diode
When the metallic region joins with N-type of semiconductor electrons form, N – material flows towards the metal, causing the heavy flow of electrons. This electron injection has very high energy compared to the metal electrons; this carrier is known as a hot carrier.
Hence the Schottky diode is also called a hot carrier diode.
Due to the flow of electrons from the N – side to metal, the region near the junction of the N – side will get depleted off the electron. The addition of a charge carrier into the metal will form a negative wall to the boundary, which causes a surface barrier between two metals results in a reduction of the flow of electrons.
When the diode is connected, supply, i.e., forward biased the majority charge carrier electrons will attract to the supply’s positive terminal. These electrons from N – side will enter into the metal, which causes the flow of electrons.
The barrier potential required to break the Schottky barrier is 0.3 to 0.5v, which means that it gives desired output current for less input voltage.
Disadvantages
- The Schottky diode has a high reverse saturation current. ( Reverse saturation current is a current flow due to minority charge carrier)
- Peak inverse voltage is low. ( peak inverse voltage is the maximum voltage that a diode can block while reverse biased)
- The operating temperature range is less.
Applications of Schottky diode
- SMPS (switch mode power supply) and communication circuits like PF mixer and detector circuit due to their high switching speed and high reverse recovery time.
- High power application where the high frequency is required.
- Switching and high power applications
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