Generally speaking, the commonly used photodiodes are also called photodiodes, which are actually very similar in structure to semiconductor diodes. We can take a closer look. The die of the photodiode is a PN junction that has photosensitive characteristics. This PN junction has unidirectional development of conductivity. Therefore, during the normal operation of the photodiode, a reverse-flow voltage is also required. Generally, when there is no light, we can see that there will be a small saturated reverse leakage current leaking out, which is what we call dark current, and the photodiode is also cut off at this time.

　　 When the photodiode is exposed to sunlight, the saturated reverse leakage current will be greatly increased, and a photocurrent will also be formed. The photocurrent will change with the specific intensity of the incident light, and the specific changes still need to be based on the operating standard. After the light irradiates the PN junction, it can also generate electron-hole pairs in the PN junction at the same time, and at the same time, it will also gradually increase the density of minority carriers.

　　 Whether the photodiode can be used normally is actually related to its manufacturing process. To know the specific work of the photodiode, it is actually a process of absorption. The photodiode converts the change of light into a developmental change of reverse current, and the combination of photocurrent and dark current is photocurrent. Therefore, the manufacturing process of the photodiode is reflected in its dark current will make the sensitivity of the device to light to the lowest level. We need the condition that the intensity of light is proportional to the photocurrent in it, so that the light signal can be converted into the correct electrical signal.