Photo Diode Working

When a photodiode is exposed to photons in the form of light, the production of electron-hole pairs is influenced. The Photodiode’s basic structure is similar to a simple PN junction diode, but it is optimised to respond to light and supports photodiode working. Because the PN junction is light sensitive, the photodiode’s PN junction to light is covered with a transparent window, allowing light to reach the photosensitive section of the PN junction. Because photodiodes have a sluggish reaction time, most of them are now made with a PIN junction rather than a PN junction to increase response time, which is often used in physics.

Definition of a photodiode

A photodiode can be defined as a device that converts light into voltage or current. This is done depending on the device’s mode of operation. Surface areas, optical filters, and built-in lenses are all provided. The response time of these diodes slows as the surface area of the photodiode increases. Photodiodes are identical to typical semiconductor diodes, except that they can be seen to let light reach the sensitive sections of the device. Instead of the more frequent PN junction, a PIN junction will be used in some photodiode diodes.

Some photodiodes have the appearance of a light-emitting diode. Two terminals protrude from the end. The cathode terminal is at the diode’s smaller end, whereas the anode terminal is at the diode’s longer end. The anode and cathode sides are depicted in the schematic image below. The conventional current will flow from the anode to the cathode under the forward bias condition, following the arrow in the diode symbol. The photocurrent flows in the opposite direction.

Photodiode Working

The principle behind a photodiode is that when a photon of sufficient energy strikes a photodiode, it forms a pair of electron-holes. The inner photoelectric effect is another name for this mechanism. If absorption happens at the depletion area junction, the depletion zone’s inherent electric field removes the carriers from the connection.

Consequently, holes in the region travel toward the anode while electrons migrate toward the cathode, causing a photocurrent to form. The sum of the photocurrent and the lack of light is the total current flowing through the diode. As a result, the missing current must be reduced to improve the device’s sensitivity.

Photodiode Working and Characteristics

Minority charge carriers continue to be swept across the junction when the reverse-bias voltage across a photodiode is withdrawn while the diode is lit. Minority carriers flow back to their original sides when an external circuit is linked across the diode terminals. The electrons crossing the p-n junction will now exit through the n-terminal and enter the p-terminal. This indicates that the device acts as a voltage cell, with the negative terminal on the n-side and the positive terminal on the p-side. A voltage can be measured on both the p-side and the n-side of the photodiode terminal, with the p-side being positive and the n-side being negative. As a result, the photodiode is a photovoltaic and a photoconductive device simultaneously, and it works on the photodiode working principle.

Operation Modes

Photovoltaic, Photoconductive mode, and avalanche diode modes are the three operating modes and work based on the photodiode working principle.

Photovoltaic Mode: Also known as zero-bias mode, this mode produces a voltage using a lightened photodiode. It has a relatively small dynamic range and necessitates the voltage being created to be non-linear.

Photoconductive mode: The photodiode is normally reverse biassed in this photoconductive mode. The reverse voltage application widens the depletion layer, lowering the response time and junction capacitance. This mode is excessively rapid and produces electronic noise.

Avalanche Diode Model: Avalanche diodes operate in a high reverse bias mode, allowing an avalanche breakdown multiplied for each photo-produced electron-hole pair. This results in a photodiode internal gain, which gradually enhances the device response.

Application of Photodiode?

Photodiodes have been used similar to photodetectors, such as charge-coupled devices, photoconductors, and photomultiplier tubes.

These diodes are found in consumer electronics such as smoke alarms, CD players, televisions, and VCR remote controls.

Photoconductors, rather than photodiodes, are more commonly employed in consumer electronics such as clock radios, camera light metres, and street lights.

In science and business, photodiodes are widely employed to precisely quantify the intensity of light. They have a more linear reaction than photoconductors in general.

Photodiodes are also widely utilised in various medical applications, including sample analysis equipment, computed tomography detectors, and blood gas monitors.

Conclusion

Photodiodes are specifically engineered to function in reverse bias situations. The P-side of the photodiode is linked to the battery’s negative terminal, while the n-side is connected to the positive terminal. Because this diode is light-sensitive, it easily converts light into an electric current when it is exposed to it.

Photodiodes are high-frequency electromagnetic radiation measurement devices that generate electrical signals in response to various high-frequency electromagnetic radiation sources, including light focused by a camera lens, ambient light, thermal emissions, laser signals used in communication systems, etc. A large-area photodiode is a solar cell that converts solar energy into electrical energy.