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Comparison of measured (circles) and calculated (solid curves) modal gain spectra in the laser structure for various excitation intensities at a temperature of . In the model, an inhomogeneous broadening of full width at half maximum and a confinement factor for the laser structure of 6.6% are included. The theoretical spectra are shifted by , matching the experiment within growth uncertainties. Carrier densities of 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, and are assumed. Experimentally, the gain spectra are obtained using the method by Hakki and Paoli at excitation currents of 12.7, 14.6, 16.9, 18.9, 20.8, and . An offset of is added to the measured spectra so that the zero line is matched; within the experimental error this vertical shift can be attributed to the outcoupling losses and internal losses of the laser. The inset shows the conversion of the experimental excitation current to the carrier density as obtained by relating the measured spectra to matching calculations.
Gain spectra modeled by microscopic theory for the (GaIn)Sb quantum well (solid lines) and a comparable GaAs-based (GaIn)As quantum well system (dashed lines) at carrier densities of 1.0, 1.25, 1.5, 1.75, and . The dash dotted lines show the gain for the (GaIn)As structure if the fundamental band gap is artificially changed to the (GaIn)Sb value of . Obviously, the gain is strongly enhanced in (GaIn)Sb, partly due to the small bandgap and partly because of band structure effects discussed in the text. The inset displays the calculated peak gain for the (GaIn)Sb quantum well structure (solid line) as well as the calculated peak gain for the (GaIn)As quantum well structure (dashed line) in dependence of the carrier density.
Band structure of the (GaIn)Sb (black solid lines) and (GaIn)As (gray dashed lines) quantum well structure. The effective band gap is shifted to matching values in the figure. In the (GaIn)Sb heterostructure, gain is enhanced by a large energetic distance between subbands and similar electron and hole masses. See the text for further explanation.
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