LEDs by Ⅲ - Ⅳ compounds, such as GaAs (gallium arsenide), GaP (gallium phosphide), GaAsP made of semiconductor such as gallium arsenide (p), it is the core of p-n junction.
Therefore, it has the general p-n junction only i-n characteristics, that is, the reverse cut-off wizard and breakdown characteristics.
In addition to its specific conditions, it also has the characteristics of luminous.
At the positive voltage, the electrons will be injected into the P region from the N region, and the holes will be injected into the N region from the P region.
The minority carriers (minority carriers) entering the opposite region are partially compounded with the majority carriers (multiple carriers) and glow.
If the luminescence is assumed to occur in the p-region, then the injected electrons and valence band holes will directly compound to produce luminescence, or they will be first captured by the luminescence center and then compound with the holes to produce luminescence.
In addition to this luminescence recombination, some electrons are captured by non-luminescent centers (which are located near the middle of the conduction and mesophase) and then recombined with the holes, releasing little energy at a time to form visible light.
The higher the ratio of the composite amount of luminescence to that of non-luminescence, the higher the efficiency of the quantum of light.
Since this recombination is luminous in the diffusion region of small particles, the light is only generated within the number of m near the PN junction surface.
Theory and practice prove that the peak wavelength of light is related to the width of band gap of semiconductor material in the luminescent area (Eg), namely lambda 1240/Eg (nm).
The unit of Eg in the formula is electron volt (eV).
If visible light can be generated (wavelength: 380nm purple light ~ 780nm red light), the Eg of semiconductor materials should be between 3.26 ~ 1.63eV.
Light whose wavelength is longer than red light is called infrared light.
There are infrared, red, yellow, green and blue leds, but blue leds are expensive and not widely used.