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There are two types of infrared receiver tubes, one is a photodiode and the other is a phototransistor. A photodiode converts light signals into electrical signals, and a phototransistor not only converts light signals into electrical signals, but also increases the discharge of electricity. Therefore, phototransistors are also divided into two types, namely NPN type and PNP type.

There is a glass lens on the shell of the infrared receiving tube that can inject light, and the incident light passes through the lens and is exactly reflected on the tube core. The infrared receiving diode core is a PN junction with photosensitive characteristics, which is encapsulated inside the shell. The photosensitive surface of the infrared receiving diode core is a thin film formed by diffusion process on N-type monocrystalline silicon.

Its tube core and PN junction area on the tube core are made larger, while the electrode area on the tube core is made smaller. The PN junction depth is shallower than that of ordinary semiconductor diodes. These structural characteristics are all aimed at improving the ability of photoelectric conversion. In addition, like ordinary semiconductor diodes, a SiO2 maintenance layer has been grown on the silicon chip, which maintains the edges of the PN junction, thereby improving the stability of the tube and reducing dark current.

In order to withstand more and larger areas of incident light, the infrared receiver tube should make the PN junction area as large as possible, minimize the electrode area, and the PN junction depth is very shallow, usually less than 1 micrometer. The infrared receiving tube operates under the action of reverse voltage. When there is no light, the reverse current is very small (usually less than 0.1 microamperes), which is called dark current. When there is infrared light, infrared photons carrying energy enter the PN junction and transfer energy to the bound electrons on the Covalent bond, making local electrons break free from the Covalent bond, thus producing electron hole pairs (photogenerated carriers for short). They participate in drift motion under the action of reverse voltage, causing a significant increase in reverse current. The greater the intensity of light, the greater the reverse current. This characteristic is called 'photoconductivity'. The current generated by an infrared receiver tube under normal illumination is called photocurrent. If a load is connected to the external circuit, an electrical signal is obtained on the load, and this electrical signal changes accordingly with the change of light.

The function of infrared receiving tube is to stop photoelectric conversion, and it is widely used in light control, infrared remote control, light detection, Fiber-optic communication, photoelectric coupling, etc.