We classify Power Diodes as shown in the figure. This classification is mainly on the basis of
- Reverse Recovery Time and the manufacturing process,
- Penetration of the Depletion Region (into the n+ layer) during the Reversed Biased condition.
Classification Based on Reverse Recovery Time and Manufacturing Process
Power Diodes are practically selected on the basis of their reverse recovery time (refer to the topic ‘Reverse Recovery Characteristics’ for the meaning of reverse recovery time) because this parameter tells how fast the diode operates i.e. the switching time (time taken for on and off process) of diode is dependent on its reverse recovery time.
Based on the Reverse recovery characteristics, diodes can be classified into 3 types
- General Purpose Diodes
- Fast Recovery Diodes
- Schottky Diodes
General Purpose Diodes
- These diodes are used for normal uses.
- General Purpose Diodes have large reverse recovery time(trr) about 25μs, hence they are used in low speed and low-frequency operations (up to 1- KHz).
Fast Recovery Diodes
- As the name suggests, these diodes have fast recovery action i.e. their reverse recovery time is very small less than 5μs.
- These diodes are used in high speed switching applications.
- Fabrication Techniques Used:
- For voltage rating above 400V – Fast Recovery Diodes are manufactured using Diffusion Process.
- For voltage rating below 400V – Epitaxy is used. Epitaxy provides faster recovery time.
- A Schottky diode is a special diode which is basically a metal-semiconductor junction diode (it is different from normal semiconductor-semiconductor junction diode e.g. pn junction diode).
- Use of only one type of semiconductor material i.e. either p-type or n-type makes it a unipolar device.
- In this diode, charge storage problem is eliminated hence it has much less reverse recovery time since only one type of charge carrier is responsible to carry current.
- With less voltage rating, Schottky diode is mostly used in low voltage and high current applications such as DC Power Supplies, Rectifiers etc.
|TYPE||VOLTAGE RATING||CURRENT RATING||REVERSE RECOVERY TIME(trr)||APPLICATIONS|
|General Purpose Diodes||50V – 5KV||1A – 1000A||25μs||Low Frequency Rectifier, Battery chargers, welding etc.|
|Fast Recovery Diodes||50V – 3KV||1A – 2000A||5μs||High – Frequency Choppers (DC-DC converter), Inverters (DC-AC converter)|
|Schottky Diodes||Up to 100V||1A – 300A||∼50ns||Low Voltage DC Power Supplies, Rectifiers|
Classification Based on Width (penetration) of Depletion Region during Reversed Biased Condition
We know that the width of the depletion region increases during the reversed biased condition and hence it tries to penetrate into the neighboring n+ layer.
Hence, Diodes can be classified as Non-punch-through and Punch-through based on the penetration (i.e. punch-through) of the depletion region into the n+ layer during Reverse Biased condition.
Non Punch Through Diodes
Diodes in which the depletion region width at the breakdown does not penetrate (i.e. punch-through) into the neighboring n+ layer are generally known as Non-punch-through diodes.
In Non-punch-through Diodes, the width of Drift Region is more than the maximum width of depletion region (at the breakdown), hence the depletion region is not able to penetrate into the neighboring n + layer.
From the analog electronics theory
Where VBD = reverse breakdown voltage
Nd = doping concentration of donor (e. n-type material)
From the above equation, if doping concentration Nd is decreased then the breakdown voltage of the diode increases e.g. if Nd= 1014 cm-3 then VBD comes out to be nearly 1000V (from the above equation).
Hence, a new layer with less doping concentration i.e. the n– Drift Region is introduced which then increases the Reverse Breakdown Voltage of the power diode.
Punch Through Diodes
Diodes in which the depletion region width at the breakdown penetrates into the n+ layer are called Punch-through diodes.
In Punch-through Diodes, the width of Drift Region is less than the maximum width of depletion region (at the breakdown), hence penetration takes place.