The core of LED is a chip composed of P-type semiconductor and N-type semiconductor. There is a transition layer between p-type semiconductor and n-type semiconductor, which is called PN junction. In the PN junction of some semiconductor materials, when the injected minority carriers recombine with the majority carriers, the excess energy will be released in the form of light, thus directly converting electric energy into light energy. When reverse voltage is applied to PN junction, minority carriers are difficult to inject, so they do not emit light. This kind of diode made by injection electroluminescence principle is called light emitting diode, commonly known as led. When working in the forward direction (that is, DC voltage is applied at both ends), when the current flows from the anode of the LED to the cathode, the semiconductor crystal emits different colors of light from ultraviolet to infrared, and the intensity of light is related to the current.
AlGaAs)- red and infrared
AlGaP)- green
AlGaInP)- high brightness orange, orange, yellow and green.
GaAsP)- Red, orange, yellow
GaP)- red, yellow, green
Gallium nitride (GaN)- green, turquoise, blue
Indium gallium nitride (InGaN)- near ultraviolet, cyan, blue
Silicon carbide (SiC) (used as substrate)-Blue
Silicon (Si) (used as substrate)-blue (under development)
Sapphire (Al2O3) (used as substrate)-blue
Zinc selenide blue
Diamond (C)- ultraviolet
Aluminum nitride (AlN), aluminum gallium nitride (AlGaN)- ultraviolet rays with far to near wavelengths.