Carrier distribution, spontaneous emission and gain engineering in lasers with nonidentical quantum wells

Novel quantum-well lasers with a 100-Angstrom GaAs quantum-well (QW) (lambd a similar to 840 nm) and a higher energy 40-Angstrom AlGaInAs QW (lambda si milar to 810 nm) in a graded AlxGa1-xAs separate confinement heterostructur e (SCN) with the bandgap increasing from the p- to the n-side are character ized. A sizeable variation in the QW carrier densities can be achieved as a function of well composition and placement due to the built-in electric fi eld that forces carriers toward the p-side of the SCH and the different den sities of states and carrier capture rates of the QW's. Transversely emitte d spontaneous emission (SE) is measured through a windowed contact to deter mine the relative contribution from each QW to the fetal SE, Information fr om these measurements is incorporated into a detailed device model to deter mine the carrier density and evaluate the gain characteristics in a ne iv w ay. Since the nonidentical wells emit different photon energies, it is show n for the first time that the carrier density can he determined at a specif ic location within the SCH of a semiconductor laser. By changing the placem ent of dissimilar QW's and the grading the SCH, it is found that the gain s pectrum can be substantially engineered.