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Difference between Schottky Diode and PN Junction Diode
A diode is an electronic device that can perform switching and rectification operation in an electronic circuit. Till date, various types of diodes have been developed with the advancement in technology.
In this article, we will discuss about Schottky diode and PN junction diode, and highlight the major differences between them by considering various parameters such as basic definition, circuit symbol, characteristics, applications, etc.
What is a PN Junction Diode?
A PN junction diode, as its name implies, a semiconductor electronic device which has two layers of oppositely charged semiconductor materials namely P-types and N-type semiconductors
These two semiconductor layers are joined together to form a PN junction. Therefore, a PN junction diode has two terminals namely anode and cathode. The anode is the terminal which is connected to the P-region while the cathode is the terminal that is connected to the N-region.
When a DC voltage is applied to the diode such that the positive terminal is connected to anode and the negative terminal of the source is connected to the cathode, then the PN junction diode is said to be forward biased and conducts the current. On the other hand, if voltage polarity is reversed, i.e. positive terminal is connected to the cathode and negative terminal to the anode, then the diode is said to be reverse biased and does not conduct the electric current.
Due to its operating characteristics, a diode is mainly used in switching and rectification applications in various electrical and electronic circuits.
What is a Schottky Diode?
A Schottky diode is a special purpose diode that uses metal to semiconductor junction for rectification applications instead of PN junction.
The semiconductor is usually silicon and metal is aluminium. Thus, in a Schottky diode, we obtain an aluminium-silicon junction. Basically, the Schottky diode is a power diode, i.e. it has higher voltage and current ratings as compared to an ordinary PN junction diode.
When the Schottky diode is forward biased, it conducts and the free electrons flow towards the metal-semiconductor junction. Since, the metal does not contain holes, therefore, in the forward bias, the conduction is only due to movement of free electrons.
The Schottky diodes are used in switching power supplies and high frequency instrumentation.
Difference between Schottky Diode and PN Junction Diode
Both Schottky diode and PN junction diode are types of electronic switching devices mainly used to perform the same function of rectification. However, there are several differences between Schottky diode and PN junction diode that are highlighted in the following table:
| Basis of Difference | Schottky Diode | PN Junction Diode |
|---|---|---|
| Description | A diode which is constructed by joining a metal and a semiconductor is called a Schottky diode. | A diode which is constructed by joining a P-type semiconductor with an N-type semiconductor is called PN junction diode. |
| Circuit Symbol |
|
|
| Junction type | Schottky diode has a metal semiconductor junction. | PN junction diode has only a semiconductor junction, which is a PN junction. |
| Terminals | In Schottky diode, the metal region forms the anode terminal and the semiconductor region forms the cathode terminal. | In PN junction diode, P-region forms the anode and N-region forms the cathode. |
| Cut-in (turn on) voltage | The turn on voltage for the Schottky diode is small, around 0.3 to 0.4 volts. | The turn on voltage of a PN junction diode is relatively high, around 0.3 to 0.7 volts. |
| Forward current | In Schottky diode, the forward current flows due to majority charge carriers only which are free electrons emitted by the metal. | In case of PN junction diode, the flow of forward current takes place due to movement of both majority and minority charge carriers. |
| Reverse leakage current | For a Schottky diode, the leakage reverse current is comparatively much larger. | PN junction diode has relatively less leakage current than a Schottky diode. |
| Depletion layer | Schottky diode has no depletion layer. | Depletion layer exists in a PN junction diode. |
| Polarity of device | Schottky diode is a unipolar device, i.e., has only one type of charge carriers namely electrons. | PN junction diode is a bipolar device having two types of charge carriers viz. electrons and holes. |
| Operating frequency | Schottky diode has higher operating frequency. | The operating frequency is comparatively lower for PN junction diode. |
| Reverse recovery time | For Schottky diodes, the reverse recovery time is nil. It is because, the metal has no holes, hence no storage of charge. | For a typical PN junction diode, there is certain reverse recovery time, ranging from 150 ns to 200 ns. |
| Switching speed | The switching speed is extremely high for a Schottky diode. | The switching speed of PN junction diode is comparatively less and is limited by recombination time of the charge carriers |
| Effect of temperature variation on switching | The switching behavior of a Schottky diode is not affected by the temperature variation. | The variation in temperature greatly influences the switching behavior of a PN junction diode. |
| PIV (Peak Inverse Voltage) | For a Schottky diode, the PIV value is much less than that of a PN junction diode. | PN junction diode has comparatively higher PIV rating. |
| Cost | Schottky diodes are slightly more expensive than PN junction diodes. | PN junction diodes are less expensive. |
| Applications | Schottky diodes are used in switching power supplies and other high frequency instrumentation. | PN junction diodes are used in general rectification and switching applications. |
Conclusion
The most significant difference that you note here is that a Schottky diode contains a metal-semiconductor junction, whereas a PN junction diode contains a PN junction.
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