Influence of Gamma-L and Gamma-X crossings on stimulated emission in AlxGa1-xAs.

The dependence of the bandstructure and the resulting dependences of the intensity and the wavelength of stimulated emission on the carrier density are demonstrated in optically excited AlxGa1-xAs near the crossover composition xc at room temperature. Density induced Gamma to L and Gamma to X crossings, based on the large band-gap renormalization near the crossover composition, are observed in samples with an AlAs mole fraction x equal 0.43 and x equal 0.46. The band crossings are indicated by strong fluctuations of the intensity and the wavelength of stimulated emission. This behavior is quantitatively well explained by using a multi-valley model for the description of the band-gap renormalization. The multi-valley model leads to an exact density-dependent prediction of the wavelength and to an estimation of the intensity of stimulated emission in indirect band-gap AlxGa1-xAs and shows the optimum AlAs mole fraction for semiconductor laser application.