In this section of video after explaining the basics of the Semiconductor and LASER, I have just tried to explain the working of Semiconductor laser that is part of a Engineering Physics Syllabus in a first year.
The idea of energy bands, the valence band and the conduction band explain briefly. Explanation of the P and N type of Semiconductor and then P-N Junction and the state of Fermi level , how it changes when join together. The depletion region and the barrier height. And then after how barrier height reduce when we apply the forward biasing which at small current behaves like a light emitting diode (LED) and when the current reach at critical value it behaves like a LASER and the transition of electron from conduction band to the valence band in the depletion region.
Follow the video tutorial below for full information.