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LED internal quantum efficiency and electro-optical efficiency principle and calculation

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LED forward voltage is applied on the PN junction, PN junction current. Electronic and hole in PN knot transition layer in the composite will produced Photon, however is not each on electronic and hole will produced Photon, due to LED of PN knot as impurities semiconductor, exists with material quality, and bit wrong factors and technology Shang of various defects, will produced impurities ionization, and fired scattering and lattice scattering, problem, makes electronic from fired State jumped moved to ground state Shi and lattice atomic or ion exchange energy Shi occurred no radiation jumped moved, is does not produced Photon, This part of the energy is not converted to convert light energy into thermal energy loss in PN junctions, so there will be a complex carrier conversion efficiency and symbol Nint said.

  LED forward voltage is applied on the PN junction, PN junction current. Electronic and hole in PN knot transition layer in the composite will produced Photon, however is not each on electronic and hole will produced Photon, due to LED of PN knot as impurities semiconductor, exists with material quality, and bit wrong factors and technology Shang of various defects, will produced impurities ionization, and fired scattering and lattice scattering, problem, makes electronic from fired State jumped moved to ground state Shi and lattice atomic or ion exchange energy Shi occurred no radiation jumped moved, is does not produced Photon, This part of the energy is not converted to convert light energy into thermal energy loss in PN junctions, so there will be a complex carrier conversion efficiency and symbol Nint said.


  Nint= (total number of photon number/composite-carrier composite carrier) x100%


  Of course, it's hard to calculate the total number and total number of photons generated composite carrier. Typically by measurement of LED light output power to assess the efficiency, this efficiency Nint is known as quantum efficiency.


  Improve internal quantum efficiency to LED manufacturing materials, PN junction and LED light-emitting layer epitaxial growth process of shine a light on the way to research could LED the Nint, after scientific and unremitting efforts in this regard has been significantly increased, from what percentage has increased to baifenzhijishi, has made considerable progress, LED the development of the future, would include better Nint wide scope.


  Assuming LEDPN knot every compound carrier to produce a photon, is not to say, LED light conversion efficiency reached 100%? the answer is no.


  From semiconductor theory can know, because different materials and epitaxial growth process of different, made from LED light wavelengths are different. Assuming the LED quantum efficiency of different light wavelengths are at 100%, but due to an electronic n-type layer and a motion to PN junction active a hole from the p-type layer movement to the active layers in PN junctions, energy e of a composite carriers required associated with LED the band at different wavelengths are different. Photon energy e is different at different wavelengths, transforms the inevitable loss of power to light, as an example to illustrate:


  For example, an in D=630nm GaInAlP four-Orange LED, its to the bias as VF ≈ 2.2V, so means it's an electron and a hole-electron potential energy required to composite into a carrier of ER=2.2Ev, and one to the potential energy of the photon as a E=Hc/of D=630nm to d ≈ one thousand two hundred and forty-six hundred and thirtieths ≈ 1.97eV, so power conversion efficiency of light energy n (E-L) =1.97/2.2x100% ≈ 90%, That is, 0.0.23eV of energy loss (EV electron volts).


  If the LED of a GaN blue 470nm, VF ≈ 3.4V, so EB ≈ 3.4EeV, EB ≈ one thousand two hundred and forty-four hundred and seventieths ≈ 2.64eV, so Nb=2.64/3.4x100% ≈ 78%, this is assuming that when you Nint=100%. If Nint=60%, then for the red LED,N (E-L) =90%x60%=54%, and n for blue LED (E-L) B=78%x60%=47s%. Visible, this is the LED light is not very high power conversion efficiency reasons.


  Have learned above LEDPN with electro-optical conversion efficiency of the active layer is not very high, there are quite a lot of energy without being converted to light energy, but is converted to thermal energy loss in PN junctions, become the source of PN junction. Adopted materials, technology and the industry is on the efforts to improve the efficiency of the mechanism. If applied to electric power on LED all photon energy, then ask: all of these photons can escape into the air "see?" answer is no. So there will be a LED photon emission rate of problems. Can be represented this way LED in the ratio of photons to escape into the air.


  Nout= (escape into the air at the photon number/PN knot have a total number of photons) x100%


  In the above formula, we can be LED quantum efficiency. To facilitate the description, we assume that LED material as GaAs, the material refraction coefficient for N1=3.9, interface is the air in contact with chips, its light refraction coefficient N0=1, laws can know from the theory of light propagation of light refraction, refraction coefficient of two different interface when you are not the same, under the reflection of light perpendicular to the interface functions are available to represent:


  R(L)=[(N1-N0)/(N1+N0)]2×100%


  For GaAs related to air, there are,


  R(L)=[(3.9-1)/(3.9+1)]2×100%=35.02


  In other words, photons are reflected back to GaAs material 35.02%, that is reflected back to the chip, cannot escape into the air, only 64.98% has the potential to spill over into the air. However, when the glow if a point light source LED, full launch critical half its boundary angle θ c related to refraction coefficient of the interface of two materials, and is determined by the following formula: θ c=Arcsin (Ndn1)


  For GaAs and air: θ c=Arcsin (1/3.9) =14.90 °


  Borders launches the critical angle for 29.8 °, at which point cannot be fired into the air, it is clear that in the case of a spherical, 8.27% range can only launch this perspective, it is clear that internal quantum efficiency is very low.


  For LED chips, of course, it's a hexahedron, is not a point light source, excluding electrode block light, the hexahedron of the six faces can have a light critical angle, a total of 49.6% out of the light area. In fact, LED due to the superior reason leads to electrodes, fixed in the lead-frame and done less than six faces to shine a light, which is short of 49.6% the launch area. LED internal quantum efficiency is only around 20%, it also has a lot of headroom, integrated LED chip structure, is to encapsulate refraction coefficient of structures, materials, and other factors to be addressed to improve light efficiency.


  In recent years because the comprehensive advantages of environmental protection, energy saving, semiconductors, LED to replace traditional light sources for general lighting fail to show restraint, but LED luminous efficiency a greater breakthrough can be achieved only if widely used, as light emitting efficiency is applied to data, to enhance the luminescence efficiency with internal quantum efficiency is closely related to electro-optical efficiency! Replacing traditional lighting must also improve driving costs down, semiconductor lighting can only be taking advantage of technology!

 
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