FREE-CARRIER ABSORPTION IN SEMICONDUCTOR-LASERS

Free-carrier absorption is theoretically studied for semiconductor las ers where the photon energy is as large as the energy gap. A quantum-m echanical investigation shows that intraband absorption is very weak a nd interband absorption totally negligible, in contrast to the usual c lassical estimations. Therefore free-carrier absorption in semiconduct or lasers is insignificant. It follows that free-carrier absorption is not the reason for the impossibility of laser action in indirect-band gap semiconductors. Obviously the scattering and mirror losses are res ponsible for this effect.