Abstract

In Al_xGa_1-xAs close to the direct-to-indirect band gap semiconductor crossover composition (x_c ≃ 0.43), alloy disorder mixes the wave functions of states in the Γ- and the X-conduction bands. This allows bimolecular recombination of electrons in the indirect bands without phonon participation (quasidirect transitions). At appropriate carrier densities stimulated emission out of the X valleys is observed for indirect Al_xGa_1-xAs with Al concentrations up to x = 0.52. In Al_0.45Ga_0.55As a population inversion for the T band is achieved for carrier densitiies at which the distribution in this band is strongly nondegenerate. This is due to the easily obtainable high degeneracy in the valence band. Simultaneous stimulated emission out of the Γ and X bands is then observed.

© 1987 Optical Society of America