Gain, refractive index change, and linewidth enhancement factor in broad-area GaAs and InGaAs quantum-well lasers

We report experimental and theoretical results for the injection-level dependence of the gain, refractive index variation, and linewidth enhancement factor (α) for four different quantum-well (QW) laser structures. Two of the lasers have GaAs QW layers that vary in width while the other two have InGaAs active layers that vary in QW depth. Experimental Hakki-Paoli data are used to compare gain, index change, and α-parameter between these pairs of devices. The results of two simulations are compared to the experimental data. The first is based on the approximation of parabolic bands for both the conduction and valence bands while the second employs the k·p method to refine the calculation of the valence bands. Our findings include: (1) narrower and deeper QWs yield lower α values; (2) modeling results from the k·p method are only slightly improved over those from the parabolic band model; (3) at high injection levels, stimulated emission below threshold is a prominent effect in these devices; and (4) at high injection levels, carriers in the barrier energy states above the well are shown to be responsible for increasing α values