The development of vertical-cavity surface-emitting lasers (VCSELs) relies on an understanding of gain-medium physics, more so than in edge-emitting lasers. An important tool in the investigation of semiconductor gain behavior is a theory that provides a systematic account of the interaction between the laser field and the electron–hole plasma, the influence of the band structure, and the many-body effects due to Coulomb interactions among carriers. This article describes a semiclassical approach that is based on the semiconductor Bloch equations, with carrier correlation effects described at the level of quantum kinetic theory. To illustrate its application, we discuss research activities involving the development of gain media for long-wavelength VCSELs.
