Physics Group - II (3110018)

Schottky diode is a metal-semiconductor junction diode that has less forward voltage drop than the P-N junction diode and can be used in high-speed switching applications. In schottky diode, the metal acts as the anode and n-type semiconductor acts as the cathode. The symbol of schottky diode is shown in the fig.1 .

1. Forward biased schottky diode:
   • If the positive terminal of the battery is connected to the metal and the negative terminal of the battery is connected to the n-type semiconductor, the schottky diode is said to be forward biased.
   • When a forward bias voltage is applied to the schottky diode, a large number of free electrons are generated in the n-type semiconductor and metal. However, the free electrons in n-type semiconductor and metal cannot cross the junction unless the applied voltage is greater than 0.2 volts.
   • If the applied voltage is greater than 0.2 volts, the free electrons gain enough energy and overcomes the built-in-voltage of the depletion region. As a result, electric current starts flowing through the schottky diode.
   • If the applied voltage is continuously increased, the depletion region becomes very thin and finally disappears.
2. Reverse bias schottky diode:
   • If the negative terminal of the battery is connected to the metal and the positive terminal of the battery is connected to the n-type semiconductor, the schottky diode is said to be reverse biased.
   • When a reverse bias voltage is applied to the schottky diode, the depletion width increases. As a result, the electric current stops flowing. However, a small leakage current flows due to the thermally excited electrons in the metal.
   • If the reverse bias voltage is continuously increased, the electric current gradually increases due to the weak barrier. If the reverse bias voltage is largely increased, a sudden rise in electric current takes place. This sudden rise in electric current causes depletion region to break down which may permanently damage the device.
3. V-I characteristics of schottky diode:
   • The V-I characteristics of schottky diode is almost similar to the P-N junction diode. However, the forward voltage drop of schottky diode is very low as compared to the P-N junction diode.
   • The forward voltage drop of schottky diode is 0.2 to 0.3 volts whereas the forward voltage drop of silicon P-N junction diode is 0.6 to 0.7 volts
   • If the forward bias voltage is greater than 0.2 or 0.3 volts, electric current starts flowing through the schottky diode.
   • In schottky diode, the reverse saturation current occurs at a very low voltage as compared to the silicon diode.
4. Advantages of schottky diode:
   • High current density
   • Low forward voltage drop or low turn on voltage
   • High efficiency
   • Schottky diodes operate at high frequencies.
   • Schottky diode produces less unwanted noise than P-N junction diode.
5. Disadvantages of schottky diode:
   • Large reverse saturation current
   • Schottky diode produces large reverse saturation current than the p-n junction diode.
6. Applications of schottky diodes:
   • Schottky diodes are used as general-purpose rectifiers.
   • Schottky diodes are used in radio frequency (RF) applications.
   • Schottky diodes are widely used in power supplies.
   • Schottky diodes are used to detect signals.
   • Schottky diodes are used in logic circuits.