Semiconductor light emitting diode has the advantages of simple structure, small volume, small working current, convenient use, low cost, so the photoelectric system application is extremely widespread.
In the forward biased semiconductor pn junction, or similar structure can emit visible light or near infrared light, the direct conversion of electric energy to light energy device called the light emitting diode, referred to as LED.
Luminous objects internal in some way to the stored energy into light radiation process. Luminous object optical radiation is material excited electron transition to the ground state is produced when the. Semiconductor (mainly in the periodic table of elements of III and V group compound semiconductor light emitting elements of the diode ) belonging to the current excitation of the electroluminescent device.
Electroluminescence phenomenon was discovered in 1923, at that time did not cause the attention of people. With the development of modern technology, light emitting device raised new requirement, hope led simple, reliable, long life, low price, small. Since 60 time begin electroluminescence studies of very active.
Atomic, molecular and some semiconductor materials, which can absorb and release a certain wavelengths of light or electromagnetic wave. According to the band theory of solid, semiconductor electron energy state is divided into the valence and conduction, when electrons from a band energy state in the E1 transition ( transfer ) to another area in the state of E2, can emit or absorb a certain frequency ( V) light. V and energy difference ( E = E2-E1 Jian ) proportional to, i.e. v = Jian E / h ( Hz )
This type is called the Bohr condition. Type in H = 6.626 * 10-34J s. When the light emitting diode when working, in forward bias, typically a semiconductor air belt is through node to which the injected electrons to occupy, the electronics and the valence band of hole recombination, photons emitted, which produces light. The photons emitted energy approximation for a particular semiconductor conduction band and valence band between the bandgap energy. This natural emission process is called spontaneous radiation composite ( Figure 1 ). Apparently, radiative transition is the composite foundation. Injected electron compound may also is not luminous, i.e. non radiative recombination. In the case of non radiative recombination of electrons in the conduction band, the lost energy can be changed into a plurality of phonon, make crystal heating, this process is called multiphonon transition; also can and the holes in the valence band composite, energy delivered to the conduction band of another electron, make its are in high energy state, and then through the process of heat balance the surplus the energy to the crystal lattice, this process is known as auger recombination. With the concentration increasing, the process will become more important. Interband transitions, radiation and non-radiative recombination of two kinds of process competition. Some light emitting materials for radiation composite dominant.