Filamentation in InGaAs quantum-dot lasers: theory and experiment

Summary form only given. One question concerning active media for semiconductor edge-emitting lasers is the behavior of the intracavity laser field (i.e., the beam quality) above threshold. Especially important are self-focusing effects which narrow the laser beam and eventually lead to beam break-up or filamentation. This paper presents theoretical and experimental results on the beam quality of edge-emitting lasers with InGaAs quantum dot active media. We use a screened Hartree-Fock theory to compute the complex susceptibility for a shallow quantum dot for different excitations. The inclusion of Coulomb effects not only influences the gain (imaginary part of the susceptibility), but also changes the dispersive behavior, i.e., the carrier induced refractive index (real part of the susceptibility) of a quantum dot active medium. Our theoretical results show that the filamentation tendency in quantum-dot lasers can be substantially weakened for sufficiently small inhomogeneous broadening, contrary to what is observed in quantum-well lasers. An indication of this is observed in our experimental results which show indeed a weaker filamentation tendency than quantum-well lasers. However, the calculations predict a still better beam quality for lasers fabricated from dot material with reduced inhomogeneous broadening.