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A two-terminal electronic component that conducts the current(I) in one direction is called a diode. In diodes, the most commonly used diode is a semiconductor diode. In this article, the special types of semiconductor diodes like photodiodes, solar cells and Zener diodes with their internal construction, their types with the application are explained.
Photodiode
Photodiodes are the special type of semiconductor diodes that convert electrical energy into light energy when exposed to light.
The junction of the photodiode is illuminated then the electric current flows through the two terminals. Only electrons flow through it when it is reverse biased. This is called the photoelectric effect.
Construction of photodiode
The PN junction of the photodiode is placed inside a glass. This transparent glass allows sunlight to pass through the diode. The other side of the glass is insulated.
Working of photodiode
When the photodiode is not exposed to light or radiation, the electrons in the p side flow through the junction. As the minority carriers are flowing through the junction, there will be a reverse current flow. This current is called dark current.
When the photodiode is exposed to light, the temperature of the junction will increase. The electrons and holes will get separated from each other. The electrons, which are in the ‘n’ side, will get attracted towards the positive terminal of the battery, and the holes, which are in the ‘p’ side, will get attracted to the (-) terminal of the battery.
As a result, a high amount of reverse current gets generated through the junction. When the light intensity increases, more carriers are generated and flow through the photodiodes. Hence, a large current is produced.
The light intensity is directly proportional to the electric current.
Applications of photodiodes
- Photodiodes are used in burglar alarms
- Photodiodes are used in counters and switching circuits
- It helps to communicate in the optical system
- It is used in logic circuits and encoders
Solar cell
A solar cell is an electrical device in which light energy gets converted into electrical energy by the photovoltaic effect. It is basically a PN junction diode and is called a photovoltaic cell. The solar panel is formed by a combination of solar cells. The common junction will produce a maximum voltage of 0.5 to 0.6 volts. Large solar panels can produce a large amount of renewable energy.
The solar cells are basically made up of materials like Gallium arsenide, Cadmium Tetride, and Silicon.
Diode construction
The solar cell is a junction diode, which contains a very thin layer of p-type semiconductor with the thicker n-type semiconductor. The PN junction layer can be found just below the p-layer.
Working of solar cell
When light is exposed to the PN junction, the light photons will enter into the junction through the p-layer. The light energy produces enough energy to create the electron-hole pairs. It is based on the breakage of the thermal equilibrium condition of the junction. The free electrons in the depletion move to the n-type side of the PN junction.
And the holes move to the p-side of the junction. The concentration of the electrons and holes will increase on both the n and p type of the junction. It will behave like a battery cell. The voltage generated is called photovoltage.
Applications of solar cell
- Used for battery charging
- Used in watches and calculators
- Used in light meters
- Provide electrical energy to spacecraft
Laser diode
A laser diode is a special type of semiconductor diode that produces coherent laser light. This light wave has the same frequency and phase. This phenomenon is called Light Amplification by Stimulated Emission Of Radiation (LASER). As it produces laser light, it is called laser diodes.
Construction Of laser diode
The laser diode is made up of P-type material, N-type material, and metal contact.
The metal plate is placed between the n and p-type layers. This is called a homojunction laser diode. The region which is used to increase the volume of active regions is called the intrinsic or active region. As a result, the holes and electrons get accumulated at the junction.
Types of laser diode
There are several types of laser diodes, such as
- Double heterostructure laser diode
- Separate confinement heterostructure laser diode
- Quantum cascade laser diode
Working of laser diode
As the current increases, the optical power of the output light increases up to the threshold. Here, the light is emitted by spontaneous emission. The power output is directly proportional to the input current.
Applications of laser diode
- Used in Laser printers
- Used in medical types of equipment
- Used in scientific instruments
- Used for cutting of materials
Zener diode and avalanche diode
Zener diode is a PN junction diode that mainly works in a reverse-biased state. The Zener diode is heavily doped.
Working on the Zener diode
The Zener diode is an ordinary diode when it is connected in forwarding bias conditions. When it is connected in reverse bias, the depletion layer becomes wider. Its width gradually increases as the reverse-biased voltage increases. The minority carriers get kinetic energy and collide with ions present in the depletion layer. More free electrons are produced, and the Zener diode becomes more conductive.
Zener breakdown
When the reverse bias voltage is applied across the pn terminals, the depletion region begins to increase. As a result, more electrons and holes are generated.
These electrons and holes produce a very powerful electric field across the junction of the diode. The magnitude of the electric field will depend on the magnitude of the applied reverse voltage.
The electric field exerts an electron force which is present in the valence band. This will enter the conduction band, and the conduction process begins.
This phenomenon is called Zener breakdown.
Avalanche breakdown
The free electrons move across the depletion region of the diode. They possess velocity, and the electrons acquire kinetic energy. Due to the presence of velocity, the minority carriers randomly move inside the diode. It collides with stationary electrons held to the atom by covalent bonding.
The covalent bonding gets broken by bound electrons, and the conduction process begins. The electrons transfer the kinetic energy to stationary electrons which makes them move. As the magnitude of the reverse bias voltage increases, the energy rises. The resulting collision produces a current, which causes the breakdown of the diode.
This breakdown is called an avalanche breakdown.
Applications of avalanche diode
The avalanche diode is used for protecting circuits against unwanted voltages. It is helpful in surge protection.
Conclusion
In this article, we have seen the special types of semiconductor diodes like photodiodes, solar cells, laser diodes, Zener diodes, and avalanche diodes. These Semiconductor diodes are used for many applications in the electronic world. And we have also covered the Zener and avalanche diodes with its breakdown theory.
