A semiconductor laser uses a semiconductor gain medium for optical amplification. Semiconductor lasers are widely used for low-power applications, particularly telecommunications applications. They can be pumped electrically or optically, but direct electrical pumping is of greater interest for most applications. Electrically pumped semiconductor lasers typically have high power conversion efficiencies, on the order of 50% or greater. A nice overview can be found here:
https://www.rp-photonics.com/laser_diodes.html
The physics of the semiconductor laser have important differences compared to those of the other laser types we’ve discussed thus far. We will explore those physics in this section.