The comprehensive semiconductor laser simulator, MINILASE, has been extended to simulate the dynamic response of vertical-cavity surface-emitting lasers (VCSELs). Various nonlinear gain effects due to carrier transport have been self-consistently accounted for by MINILASE and their important roles in the modulation response are studied and clarified. First, it is demonstrated that a roll-off in the modulation response is closely associated with the diffusion capacitance caused by vertical carrier leakage. This effect is greatly suppressed by either grading the separate confinement regions or reducing their thickness. Second, it has been identified that, due to the nonuniform optical intensity, carriers at different locations in the quantum well (QW) have different stimulated recombination rates. Therefore, they exhibit a different dynamic response to small signal modulation. This nonuniformity causes an over-damping of the relaxation oscillations as well as a low frequency roll-off. To crystallize the underlying physics, a coupled one-dimensional rate equation model has also been developed. We further demonstrate that this damping effect can be significantly reduced by restricting the current injection area to the area of large transverse optical field. This is achievable by using tapered oxides to make the electrical aperture smaller than the optical aperture. Third, an additional energy balance equation has been added to MINILASE to solve the QW carrier temperature. It is shown that the dual modulation of the carrier temperature and quasi-Fermi level leads to an severe damping effect in the modulation response, and thereby further reduces the maximum bandwidth of VCSELs.
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