Introduction to Semiconductor LASER
In this video tutorial of semiconductor LASER the following points which given below are explained. The GaAs is responsible for the optical properties when electron and holes recombines in depletion region. As you know in Si/Ge semiconductor material when this recombination take place heat produces and at high current the components burn.
When we add tri-penta valent doping impurities in pure semiconductor it forms P and N type semiconductor. Here both type of semiconductors are heavily dopped by the impurities. Represented by n+ and p+ semiconductors.
The concept which we use here to explain the working of the semiconductor LASER is the energy band diagram of the p and n junction. The Fermi energy concept is useful here to explain about the filled and unfilled energy levels by the electrons.
In the absence of external current source (battery) the Fermi energy level remain just above the valence band in p type semiconductor while in n type of semiconductor it remains below the conduction band. In a pn junction diode the Fermi energy level remain in equilibrium, uniform in both sides. With changing there position that you can see in best way through the picture towards p and n side in energy band diagram.
When we provide the forward biasing then the potential barrier decreases and further majority charge carriers from n and p side get the space in depletion region where they get diffused and as a result photons emit. These emitted photons move in all direction but when forward current reaches the threshold value it starts to emit photons in unidirectional.
The earlier case is of the Light Emitting Diode (LED) while beyond the threshold value of current it works for LASER. Now for more detail please watch the video. If you have any doubt or questions you can ask in the comment box.