What is a PIN photodetector

What is a PIN photodetector

A photodetector is precisely a highly sensitive semiconductor photonic device that converts light into electricity by utilizing the photoelectric effect. Its main component is the photodiode (PD photodetector). The most common type is composed of a PN junction, corresponding electrode leads and a tube shell. It has unidirectional conductivity. When a forward voltage is applied, the diode conducts; when a reverse voltage is applied, the diode cuts off. PD photodetector is similar to a common semiconductor diode, except that PD photodetector operates under reverse voltage and can be exposed. It is packaged through a window or optical fiber connection, allowing light to reach the photosensitive part of the device.

Meanwhile, the most commonly used component in PD photodetector is not the PN junction but the PIN junction. Compared with the PN junction, the PIN junction has an additional I layer in the middle. The I layer is a layer of N-type semiconductor with a very low doping concentration. Because it is an almost Intrinsic semiconductor with a low concentration, it is called the I layer. Layer I is relatively thick and almost occupies the entire depletion region. The vast majority of incident photons are absorbed in the I layer and generate electron-hole pairs (photogenerated carriers). On both sides of the I layer are P-type and N-type semiconductors with very high doping concentrations. The P and N layers are very thin, absorbing a very small proportion of incident photons and generating a small number of photogenerated carriers. This structure can significantly accelerate the response speed of the photoelectric effect. However, an overly wide depletion region will prolong the drift time of photogenerated carriers in the depletion region, which instead leads to a slower response. Therefore, the width of the depletion region should be reasonably selected. The response speed of the PIN junction diode can be changed by controlling the width of the depletion region.

The PIN photodetector is a high-precision radiation detector with excellent energy resolution and detection efficiency. It can accurately measure various types of radiation energy and achieve rapid response and high stability performance. The function of the photodetector is to convert the two light wave signals after the beat frequency into electrical signals, eliminate the additional intensity noise of the local oscillator light, enhance the intermediate frequency signal, and improve the signal-to-noise ratio. PIN photodetectors feature a simple structure, ease of use, high sensitivity, high gain, high bandwidth, low noise, and strong anti-interference ability. They can operate stably in various harsh environments and are mainly applied in wind measurement lidar signal detection.