Strained-Layer Quantum-Well Lasers

This tutorial article explains the two important reasons for the introduction of strain into the active region of a quantum-well laser. First, it reduces the density of states at the top of the valence band, which allows population inversion to be obtained at a lower carrier density. Second, it distorts the 3-D symmetry of the crystal lattice and matches it more closely to the 1-D symmetry of the laser beam. Together these effects greatly enhance almost all characteristics of semiconductor lasers and make possible a wide range of applications. Combinations of compressive and tensile strain can also be used, for example, to produce nonabsorbing mirrors and polarization-insensitive semiconductor optical amplifiers.