PIN photodiode is a kind of semiconductor device made of P-I-N structure, which can convert optical signal into electrical signal, and can change with the change of light. In view of the shortcomings of conventional PD, its structure has been improved, and its sensitivity is higher than that of conventional P-N junction photodiodes, and it has unidirectional conductivity characteristics.

　　 The commonly used silicon photovoltaic cells in the market generally work in the visible light band. The photoelectric conversion rate of monocrystalline silicon is about 18%, and the photoelectric conversion rate of polycrystalline silicon is about 16%. The signal-to-noise ratio is generally not considered. The time constant of silicon battery is large, the instantaneous speed is slow, and the manufacturing cost is high.

　　 Compared with silicon batteries, PIN photodiodes have superior performance:

　　 1. A wide range of light-sensitive wavelengths, new smart PIN diodes, 400nm-1000nm;

　　2, high signal-to-noise ratio;

　　3, faster response speed;

　　 4. Low cost;

　　 5. More stable;

　　6. High frequency, very suitable for fast-changing optical signal detection.

　　 When choosing a photodiode, many factors need to be considered, including the size of the photodiode, capacitance, noise, dark current, and package type. Generally speaking, choose a smaller photodiode with a reflector or lens that can focus the light source.