Impact of well coupling on the spontaneous emission properties of GaAs/AlGaAs multiple-quantum-well structures

The impact of well coupling on the emission spectra of multiquantum-well structures is discussed. Luminescence experiments are performed in the temperature range between 1.5 K and room temperature and at various excitation densities. High-excitation room temperature results are used for the calculation of gain profiles. With increasing coupling strength a transition from two-dimensional to three-dimensional behavior of the charge carriers is observed. In particular the two-dimensional gap is lowered, the light-hole-heavy-hole splitting is reduced, the influence of interface roughness on the line shapes is reduced, excitons cease to dominate the room-temperature luminescence, and the low-temperature recombination process switches from a non-k -conserving to a k-conserving one. Some of the fundamental advantages of quantum-well lasers, such as the improved TE/TM mode selection, the small spontaneous-to-stimulated emission ratio, and the tendency towards single-longitudinal-mode operation, are gradually lost. A detailed theory of electronic states in superlattices and of superlattice emission line shapes quantitatively explains these results