A Schottky diode is a metal-semiconductor junction (M-S) diode that has less forward voltage drop than the P-N junction diode and can be used in high-speed switching applications. The forward voltage drop of the silicon P-N junction diode is 0.7 volt.
The forward voltage drop of the Schottky diode is 0.3 volts similar to the germanium P-N junction diode. But germanium diodes are rarely used because the switching speed of germanium diodes is very low as compared to the switching speed of Schottky diodes.
In the P-N junction diode, the conduction takes place through the majority carriers. However, if the minority carrier once injected into the region it is difficult to remove these charge carriers and because of these stored charges the device takes more time to go into the off state.
The turn off time of the device increase when the charges get stored in the depletion region. The turn off time of the Schottky diode is very less as compared to the P-N junction diode and this feature of the Schottky make it suitable for the high-frequency application.
The Schottky diode is connected across the collector and the base junction to prevent the BJT to go into the saturation, and to improve the switching characteristic of the BJT. The logic family using this technology is called Schottky TTL. The symbol of schooky diode is as given below.
Schottky Diode Working Principle
The Schottky diode has a metal to semiconductor junction. In Schottky diode, metals such as aluminum or platinum replace the P-type semiconductor. The N-type semiconductor acts as a cathode and the metal side acts as the anode of the diode.
The Schottky diode is named after German physicist Walter H. Schottky. A Schottky diode is also known as Schottky barrier diode, surface barrier diode, a majority carrier device, hot-electron diode, or hot carrier diode. Schottky diodes are widely used in radio frequency (RF) applications.
When the metal like aluminum or platinum is joined with N-type semiconductor, a junction is formed between the metal and N-type semiconductor. This junction is known as a metal-semiconductor junction or M-S junction.
A metal-semiconductor junction formed depletion layer known as a Schottky barrier. The Schottky diode can switch on and off much faster than the p-n junction diode because the junction capacitance of the schottky diode is very less compared to the junction capacitance of the P-N junction diode.
Also, the Schottky diode produces less unwanted noise than p-n junction diode. These two characteristics of the Schottky diode make it very useful in high-speed switching power circuits.
The voltage drop across of a silicon P-N junction is 0.6 to 0.7 volts, while a Schottky diode has a less voltage drop of 0.2 to 0.3 volts. The less voltage drop in the Schottky diode leads to higher efficiency of the diode.
Operation of Schottky Diode
The free electrons from the n-type semiconductor move from n-type semiconductor to metal during the combination process when the schottky diode is unbiased.
V-I Characteristics Of Schottky Barrier Diode
The V-I characteristics of a Schottky barrier diode are as given below.
- The forward voltage drop of the Schottky barrier diode is very low as compared to a normal PN junction diode.
- The forward voltage drop ranges from 0.3 volts to 0.5 volts.
- With increase of T N- type semiconductor concentration, the forward voltage drop increase.
- The V-I characteristics of a Schottky barrier diode are very steeper compared to the V-I characteristics of normal PN junction diode due to the high concentration of current carriers.
Applications Of Schottky Diode
Schottky diodes are used for the following purposes.
- Voltage clamping applications and prevention of transistor saturation
- Used for RF applications.
Advantages Of Schottky Diode
- Low turn-on voltage: The turn-on voltage for the diode is between 0.2 and 0.3 volts. For a silicon diode, it is against 0.6 to 0.7 volts from a standard silicon diode.
- Fast recovery time: A fast recovery time means a small amount of stored charge that can be used for high-speed switching applications.
- Low junction capacitance: It occupies a very small area, after the result obtained from wire point contact of the silicon. Since the capacitance levels are very small.