Influence of effective mass and energy band splittings on the radiative characteristics of QW lasers at transparency

The effect of degenerate light- and heavy-hole bands on the carrier and current density and the differential gain are studied and compared with the nondegenerate case in semiconductor quantum-well(QW) lasers. It is demonstrated that the presence of the degenerate bands at the valence band (VB) maximum will always lead to an increased threshold radiative current density compared to the case where only one band is significantly populated. When the valence bands are separated by an energy E-s, the current density decreases rapidly with increasing E-s, with greater reductions being achieved for a given tensile than compressive strain. The effect of the second subband becomes less important with increasing E-s, and the radiative current density reverts to that of the one VB case, demonstrating the importance of maximising the subband energy separation to optimize laser characteristics. (C) 1999 Elsevier Science B.V. All rights reserved.