Engineering Physics

10.8 Semiconductor lasers

A highly doped p-n junction diode made up of direct band gap semiconductor material under forward bias emits photons from the junction due to the recombination of conduction band electrons and valence band holes. Example for direct band gap semiconductor is GaAs. During recombination a conduction band electron crosses the energy gap (E_g) and combines with a hole present in the valence band. A photon of energy, hν equal to E_g is released. Hence . Where h = Planck’s constant = 6.63 × 10^–34 J-S; C = velocity of light = 3 × 10⁸ m/s and λ = wavelength of emitted photon. In semiconductors, p-n junction is the active region to ...