Schottky diodes are a type of metal-semiconductor junction diode, also known as hot carrier diodes, low voltage diodes, Schottky blocking diodes, surface blocking diodes, and majority carrier diodes. A scientist named Walter H. Schottky first discovered the Schottky diode.
Generally in PN junction devices, connecting a positive type (p-type) and a negative type (n-type) forms a PN junction. However, Schottky diodes use materials such as aluminum and platinum instead of P-type semiconductors.
Features of Schottky Diode
- Low forward voltage drop
- Fast recovery time
- Low-loss energy at higher frequencies
- It is a Uni-polar device
Symbol of Schottky Diode
Construction of Schottky Diode
- A Schottky diode creates a metal-semiconductor transition, known as a Schottky barrier, between the metal material and the semiconductor.
- Some silicons including gold, platinum, tungsten, and N-doped semiconductor materials are used in the construction of this diode.
- The metal part of this diode acts as the anode and the N part as the cathode, so the average current can move from the metal part to the semiconductor following the conventional current direction.
- The diode’s Schottky barrier ensures fast switching and low forward-bias voltage leakage.
- The required forward voltage of the diode depends on the metal and semiconductor materials used. Both N-type and P-type semiconductor materials can be used to create Schottky barriers, but P-type materials have lower forward bias.
- As the forward bias voltage decreases, the reverse leakage current increases, thus keeping the voltage value in the range of 0.5 to 0.7 volts for P-type materials.
V-I Characteristics of Schottky Diode
The V-I (voltage-current) characteristics of a Schottky diode are shown below. Along the graph, vertical lines represent current flow and horizontal lines represent voltage across the Schottky diode. Schottky diodes have a V-I characteristic similar to that of PN junction diodes.
Nevertheless, the forward voltage drop of Schottky diodes is very small compared to PN junction diodes. The forward voltage drop ranges from 0.3 volts to 0.5 volts. The forward voltage drop barrier is made of silicon. The forward voltage drop is proportional to the doping concentration in N-type semiconductors. The Schottky diode has a steeper V-I characteristic due to the higher concentration of current carriers.
Working of Schottky Diode
Schottky diodes are primarily known for their fast switching speed and low forward voltage drop. Furthermore, there is no depletion layer at the junction between the metal electrode and the semiconductor, so the diode cannot store additional charge at the junction as it is for PN diodes. So every time the voltage drops, current flows directly through the diode.
Advantages of Schottky Diode
- The diode capacitance is small because the diode depletion region is negligible.
- The diode reverse recovery time is very fast. That is, the transition from the ON state to the OFF state is fast.
- The diode has a high current density because the depletion region is negligible.
- The diode turn-on voltage is 0.2 to 0.3 volts, which is very low.
The disadvantage of Schottky Diode
- Reverse saturation of current is very large
Application of Schottky Diode
- RF mixer and detector diode
- Power divider in OR circuit
- As a rectifier in the power supply of Solar Panels
- Voltage clamp to prevent transistor saturation
- The high-speed switching mechanism allows his TTL of digital devices such as computers and laptops