The terminal voltage of the PN junction constitutes a certain potential barrier. When a forward bias voltage is applied, the potential barrier drops, and the majority carriers in the P and N regions diffuse to each other. Since the mobility of electrons is much greater than that of holes, a large number of electrons will diffuse to the P region, which constitutes the injection of minority carriers in the P region. These electrons recombine with the holes in the valence band, and the energy obtained during the recombination is released in the form of light energy. This is the principle of PN junction light emission.
