Light emitting diodes, like ordinary diodes, are composed of a PN junction and also have single conductivity. When a forward voltage is applied to the light-emitting diode, the holes injected from the P region into the N region and the electrons injected from the N region into the P region recombine with the electrons in the N region and the holes in the P region within a few micrometers near the PN junction, respectively, producing spontaneous emission fluorescence. The energy states of electrons and holes in different semiconductor materials are different. When electrons and holes recombine, the amount of energy released varies. The more energy released, the shorter the wavelength of the light emitted. Commonly used are diodes that emit red, green, or yellow light. The reverse breakdown voltage of the light-emitting diode is greater than 5 volts. Its forward volt ampere characteristic curve is very steep, and when used, a current limiting resistor must be connected in series to control the current passing through the diode.
The core part of a light-emitting diode is a chip composed of P-type and N-type semiconductors, with a transition layer between the P-type and N-type semiconductors called a PN junction. In the PN junction of certain semiconductor materials, when the injected minority carriers recombine with the majority carriers, excess energy is released in the form of light, thereby directly converting electrical energy into light energy. PN junction with reverse voltage makes it difficult to inject a few carriers, so it does not emit light. When it is in a forward working state (i.e. with a forward voltage applied at both ends), when the current flows from the LED anode to the cathode, the semiconductor crystal emits different colors of light from ultraviolet to infrared, and the strength of the light is related to the current.