Silicon photodetectorIt is a photoelectric conversion device based on silicon materials, whose core principle is to use the photoelectric effect of silicon to convert optical signals into electrical signals.
Working Principle:
Light absorption: When light is irradiated onto a silicon photodetector, photon energy is absorbed by the silicon material.
Electron excitation: The absorbed light energy excites electrons in silicon to the conduction band in the energy band, forming electron hole pairs.
Carrier separation: Due to the semiconductor properties of silicon, electrons and holes are separated under the action of an external electric field.
Current generation: Separated electrons and holes form a current along a conductor under the action of an electric field. The current signal generated by the photoelectric conversion process can be measured through electrodes connected to an external circuit.
Silicon photodetectorAccording to different structures and working principles, it can be mainly divided into the following types:
Photoconductive detector: made using the photoconductive effect of semiconductor materials. When the voltage passes through the detector, the incident photons generate charge carriers, which are swept by the applied electric field and transmitted to the terminals of the device. Metal semiconductor metal (MSM) detector is a structure in photoconductive detectors that has low capacitance characteristics and fast transmission speed, up to 300GHz.
PIN detector: It is currently the most widely used structure in silicon photonics. One side of the detector is p-type (positive), and the other side is n-type (negative). P-type and N-type are heavily doped, while the intrinsic region is undoped or low doped. The PIN structure creates a built-in electric field in the intrinsic region, where light is absorbed and electron hole pairs are generated. Under the action of the electric field, electrons drift towards the N region and holes drift towards the P region, resulting in photocurrent. PIN detectors also have responsiveness at 0V, but typically an additional reverse bias voltage is applied to maximize responsiveness.
Avalanche detector (APD): The maximum responsivity of both photoconductive and PIN detectors is limited by the bandgap width of the absorbing layer material. Avalanche detectors improve quantum efficiency through avalanche gain. When carriers collide at high energy, additional electron hole pairs are generated, and this reaction continues to occur, resulting in a significant increase in the number of generated carriers. In avalanche photodetectors, the photocurrent generated by charge carriers is amplified many times by the charge carriers generated by the avalanche.