The working principle and main characteristics of photodiodes

A photodiode is a semiconductor device that can convert optical signals into electrical signals. It converts incident light energy into electrical energy through the photoelectric conversion effect, thereby generating current. Photodiodes are widely used in fields such as photodetection, communication, and optoelectronic measurement. The following will provide a detailed introduction to the working principle and main characteristics of photodiodes.

1. Working principle of photodiode:

The photodiode adopts a PN junction, and its working principle is mainly based on built-in electric field and photoelectric effect.

The photoelectric effect refers to the transfer of energy to matter when photons interact with it, causing electrons to transition from the valence band to the conduction band, forming a photo generated carrier. When the photon energy is greater than or equal to the bandgap energy of the material, the generation of photo generated charge carriers will significantly increase.

In the PN junction, the P region is enriched with impurities, while the N region is doped with impurities. When forward bias and reverse bias are applied on both sides of the PN junction, i.e. Vd>0 and Vd<0, the photodiode can operate.

When forward biased, due to the presence of more charge carriers in the P region, the photodiode will enter a conducting state with a large reverse current. When light shines on the PN junction, the number of photo generated carriers increases, leading to an increase in current.

When reverse biased, the electric fields in the P and N regions form a potential barrier, causing the photodiode to be in a cut-off state with only a very small reverse saturation current. When light shines on the PN junction, the photo generated carriers move under the driving force of the electric field, resulting in a weak reverse current.

2. Main characteristics of photodiodes:

(1) Optoelectronic response speed: Photodiodes have a fast response speed and can achieve high-frequency signal reception and transmission. This depends on the generation, diffusion, and collection rates of photo generated charge carriers.

(2) Spectral response range: Different types of photodiodes have different response capabilities to light of different wavelengths. Common photodiodes include visible light and infrared light. The wavelength range determines the application field of photodiode s.

(3) Quantum efficiency: Quantum efficiency refers to the efficiency of a photodiode  in converting incident light into electrons. It depends on the material and structural design of the photodiode , generally ranging from 10% to 90% in the visible light range.

(4) Linearity: The linearity of a photodiode  refers to the degree of linear relationship between the input optical signal and the output current. Good linearity can ensure the accuracy and stability of photoelectric conversion.

(5) Dark current: Dark current refers to the current generated by a photodiode  itself in the absence of light irradiation. The smaller the dark current, the higher the sensitivity of the photodiode .

(6) Response time: Response time refers to the time it takes for a photodiode  to receive a light signal and generate the corresponding current. Short response time means that photodiode s can quickly respond to changing light signals.

In short, photodiode s convert light energy into electrical energy through the photoelectric effect, and have the characteristics of fast response, high quantum efficiency, and wide spectral response range. This makes photodiode s an important device in the fields of photodetection and communication.