Like Zener diode, avalanche diode is a semiconductor diode that operates especially in the reverse-biased region. It is a type of PN junction diode having the same symbol as the Zener diode. The avalanche diode is designed in such a way that it can withstand the avalanche breakdown without being damaged by the suddenly and sharply increased reverse current.
It is seen that a normal PN junction diode gets damaged due to an increase in temperature caused due to sudden high rise in the current. To prevent such damages to the diode in specific applications, the avalanche diodes are designed and used.
Avalanche diode symbol
The symbol of an avalanche diode is shown in figure 1.
An avalanche diode has two terminals i.e. anode and cathode. It is made up of P-type and N-type semiconductor material. It works under reverse-biased condition.
The doping of the avalanche diode differs from a Zener diode. The avalanche diode is doped lightly unlike a Zener diode and hence it forms a depletion layer having a high width. Since the width of the depletion layer decides the breakdown voltage in a diode. Therefore, the avalanche breakdown voltage occurs at a higher voltage than the Zener breakdown voltage.
Avalanche diode working
The operation of avalanche diode in the forward biased condition is similar to the normal PN junction diode. It also allows current to flow in the reverse biased condition when the reverse voltage greater than the reverse breakdown voltage is applied. This is due to avalanche breakdown. Hence it is generally used in the reserve biased condition.
The avalanche diode is in the reverse-biased condition, done by connecting the positive terminal of the source with the N-type material of the diode and the P-type material of the diode with the negative terminal of the source.
When a reverse voltage is applied to this diode, a small reverse leakage current flows through the diode due to minority charge carriers. When this reverse-biased voltage is increased further, it induces a strong electric field in the depletion region; the energy gain by the minority charge carrier increases. This results in the fast movement of minority charge carriers.
These fast-moving minority charge carriers collide with the atoms and detach valence electron from the atom. Now this valence electron becomes free. This process happens continuously. This causes a large number of electrons to free from the atoms. This will result in an increase in the reverse current through the PN junction. As the applied voltage reaches the voltage, known as avalanche breakdown voltage, the diode enters the breakdown condition. A large reverse current increases rapidly. This type of breakdown where carriers multiply is known as avalanche breakdown. As the word avalanche means large mass, hence the production of the large current due to the avalanche breakdown is known as avalanche current.
The characteristic of the avalanche diode is almost similar to that of the Zener diode. The avalanche breakdown occurs because of the minority carriers present in the junction. The avalanche diodes are constructed in such a way that the voltage drop that occurs in the breakdown region is less than the voltage drop in the Zener diode.
The I-V characteristic of an avalanche diode is shown in figure 2.
Avalanche diode advantages
The advantages of an avalanche diode are
1. It protects the diode from being damaged by the highly increased current and increased temperature.
2. The avalanche breakdown current gets multiplied and gives a high current.
3. The diode protects the devices from the damages caused by excessive voltages.
4. The performance of the diode is high.
5. The doped in the semiconductor materials used for the construction of the avalanche diode is low.
6. The avalanche diode exhibits the multiplication effect and increases the current.
Avalanche diode disadvantages
The disadvantages of the avalanche diodes are
1. The output of the diode is non-linear.
2. The required avalanche breakdown voltage is higher than the Zener breakdown voltage.
3. The reliability is low.
4. Noise production in this diode is higher than that of a normal PN junction diode.
Avalanche diode applications
The applications of an avalanche diode are
1. In order to protect a circuit, the avalanche diode is used. Due to the avalanche effect, the diode exhibits protection against the high rising current.
2. The diode works smoothly without being damaged at high temperature.
3. To protect the devices connected to the circuit from the excessive voltage, an avalanche diode is connected to the circuit.
4. The avalanche diode is used to generate calm and relaxing noise.
5. In the radio gear, these diodes are used as noise generator for the radio-frequency devices.
6. The avalanche diode is used in microwave frequency detection as it acts as a negative resistance device.
7. The avalanche diode is used as a single-photon detector in various applications.
8. The devices that require high current use avalanche diode as it has current multiplication capacity.