INCORPORATION OF STRAIN INTO A 2-DIMENSIONAL MODEL OF QUANTUM-WELL SEMICONDUCTOR-LASERS

We have incorporated the effect of strained quantum wells into our two-dimensional (2-D) semiconductor laser simulator. An anisotropic parabolic band structure is used to approximate the valence band structure obtained from a Luttinger-Kohn k.p theory to facilitate the simulation. We show that, with a proper choice of the anisotropic effective masses, a good approximation of the strained band structure can be obtained. This approximation allows us to model the gain, spontaneous emission rate, and the carrier concentration in a form usable in our 2-D laser simulator. With the improved 2-D model we are able to study the effects of strain and geometric effects in a consistent manner. Here we demonstrate the usefulness of such a 2-D model with an example of a ridge-waveguide strained InGaAs-AlGaAs laser. Our simulation shows that for compressive strain the gain function is enhanced significantly, but so too are the spontaneous emission and the leakage current. The predicted effect of strain on the lasing threshold is in good agreement with experimental results. While strain affects the threshold current, the degrading effects of geometric current spreading are still dominant in a ridge-waveguide laser. Through optimization of the GaAs layer thickness, we show that an optimal optical confinement does not necessarily correspond to an optimal threshold current.