Solid State Electronic Devices, 7th Edition

8.4 Semiconductor Lasers

The laser became an important part of semiconductor device technology in 1962 when the first p-​n junction lasers were built in GaAs (infrared)⁵ and GaAsP (visible).⁶ We have already discussed the incoherent light emission from p-​n junctions (LEDs), generated by the spontaneous recombination of electrons and holes injected across the junction. In this section we shall concentrate on the requirements for population inversion due to these injected carriers and the nature of the coherent light from p-​n junction lasers. These devices differ from solid, gas, and liquid lasers in several important respects. Junction lasers are remarkably small (typically on the order of 0.1 ⨉ 0.1 ⨉ 0.3 mm), they exhibit high efficiency, ...