Light Source Materials

In light source materials the spontaneous emission is due to the carrier recombination called as the carrier recombination of electroluminescence.  

To encourage electroluminescence is necessary to select an appropriate semiconductor type of  material. The semiconductors depending on energy band-gap can be categorized into the following way :
  • Direct band-gap semiconductors 
  • Indirect band-gap semiconductors. 
  • Indirect band-gap semiconductors, electrons, and also holes on either side of band gap have the same value of crystal momentum. Hence, direct recombination is ban possible
  • In the indirect gap semiconductors, the maximum and minimum energies occur at different values of crystal momentum. The recombination in these semiconductors is quite slow.
  • In this laser, the active layer semiconductor material must have a direct band gap. Indirect bandgap semiconductor, electrons, and also holes recombine directly without need of the third particle to conserve momentum.
  • In these materials, the optical radiation is sufficiently too muchhigh. 
  • The peak output power is obtained at (810 nm ) The width of emission at half power (0.5) is referred to as (full-width half maximum (FWHM spectral width. For the given LED FWHM is 36 nm.
The fundamental quantum mechanical relationship between the gap energy E and frequency v is given as :

 E = hv

 E = hc / ɣ

 ɣ = hc / E


Where energy = joules, and wavelength = meter.  So expressing the gap energy in electron volts and wavelength in micrometers for this application.