PN junction LED forward voltage is applied to the PN junction will have current through the electron and hole in the PN junction transition layer composite will produce photons. However, not each produce photons, electrons and holes are as impurities in semiconductor PN junction, there is the quality of materials, dislocation of factors as well as flaws in the process, will produce impurity ionization, excitation scattering and lattice scattering problem, the electron from the excited state transition to the ground state energy exchange with the lattice atoms or ions nonradiative transition occurs, that is, does not produce photons, this part of the energy is not converted into light energy is converted into heat loss in the PN junction, so there a composite carrier conversion efficiency to Nint symbol represents.
The number of photons generated by the Nint = (composite carrier / composite total number of carriers) × 100%
Of course, it is difficult to calculate the total number of the composite carrier, and the total number of photons generated. Is generally evaluated by measurement of the optical power of the LED output the efficiency, that this efficiency the Nint called internal quantum efficiency.
Improve internal quantum efficiency from the LED manufacturing material the PN junction epitaxial growth process, and LED light-emitting layer, a light way to study may improve the LED Nint this regard through the tireless efforts of the scientific community has increased significantly from the early a few per cent up to several tens of percent, has made substantial progress, the future development of LED, there is to improve Nint much space.
Assuming that the PN junction of each composite carrier can produce a photon, and is not to say, LED electric light conversion efficiency reaches 100%? Answer is negative.
Can know, is different due to the different materials and the different epitaxial growth process, the emission wavelength of the LED's made from the semiconductor theory. Assuming its internal quantum efficiency of these different light emitting wavelength of the LED to reach 100%, but due to an electronic N-type layer is moved to the active layer of the PN junction and a layer movement of holes from the P-type active layer to the PN junction, to produce a composite carrier LED's of the sub-required energy E and a different wavelength band position related not the same. The different wavelengths of the photon energy E is different, the inevitable loss of electrical energy to the conversion of light energy, the following example will be described:
E.g. one into D = 630nm of GaInAlP four yuan orange LED, its forward bias VF ≈ 2.2V so required means that it is of an electron and a hole are combined into one carrier of electrical potential energy ER = 2.2Ev , while the one into D = 630nm of the potential energy of the photon is E = hc / into D ≈ 1240/630 ≈ 1.97eV, so the electric energy to optical energy conversion efficiency of N (EL) = 1.97/2.2 × 100% ≈ 90%, i.e. 0.0.23eV energy loss (EV electron volts).
If a GaN Blu 470nm LED, VF ≈ 3.4V, so EB ≈ 3.4EeV, while EB ≈ 1240/470 ≈ 2.64eV, so Nb = 2.64/3.4 × 100% ≈ 78%, it is assumed Nint = 100%. If Nint = 60%, then for the red LED, N (EL) = 90% × 60% = 54%, and for the blue LED N (EL) B = 78% × 60% = 47s. Visible, which is not very high, the LED light power conversion efficiency reasons.
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