Electronics & Software – Tips & Guide


How does photodiode detect light?

How does photodiode detect light?

LEDs can also be used as photodiodes because they can emit and sense light from their junction. All PN junctions are photosensitive and can be used in a photoconductive, undistorted voltage mode with the PN junction of the photodiode always reverse biased so that only the diodes can leak or dark current flow.

The working principle of a photodiode is that when a photon hits the diode with great energy, it forms an electron hole. This mechanism is also referred to as an internal photoelectric effect. When the absorption occurs in the barrier layer, the carriers are removed from the barrier layer by the built-in electric field of the barrier layer.

Therefore, holes in the region move toward the anode and electrons toward the cathode, and a photocurrent is generated. The total current through the diode is the sum of light failure and photocurrent. Therefore, the missing current must be reduced to maximize the sensitivity of the device.

How does photodiode respond to solar light?

Photodiodes are semiconductor devices that are designed to detect light and convert it into an electrical current. When exposed to solar light, which consists of a broad spectrum of wavelengths, photodiodes respond in the following manner:

1. Absorption of photons: Photodiodes are constructed with a light-sensitive semiconductor material, such as silicon. When photons from solar light interact with the semiconductor material, they can be absorbed by the material. The energy of the absorbed photons is transferred to the electrons in the material, promoting them to a higher energy state.

2. Generation of electron-hole pairs: The absorbed photons create electron-hole pairs within the semiconductor material. The energy from the photons causes electrons to break free from their atomic bonds, leaving behind positively charged holes. This process is known as photoexcitation or photogeneration.

3. Separation of charge carriers: The newly created electron-hole pairs become separated due to the internal electric field within the photodiode. The negatively charged electrons move toward the n-type region of the photodiode, while the positively charged holes move toward the p-type region.

4. Current flow: The separated charge carriers result in a flow of current within the photodiode. The magnitude of this photocurrent is proportional to the intensity of the incident solar light. The photocurrent can be measured and used to determine the light intensity or as a basis for further signal processing.

It’s important to note that photodiodes have a limited spectral range of sensitivity. Different types of photodiodes are optimized for specific wavelength ranges, and their responsivity varies across the spectrum. For example, silicon photodiodes are sensitive to visible and near-infrared light, while other materials, such as gallium arsenide or indium gallium arsenide, are used for extended sensitivity into the infrared range.

By utilizing the response of photodiodes to solar light, they are commonly employed in various applications, including solar energy monitoring, light sensing, optical communication systems, and environmental monitoring.