Strain-dependent optical emission in ${\mathrm{In}}_{1-x}{\mathrm{Ga}}_x\mathrm{A}\mathrm{s}/\mathrm{I}\mathrm{n}\mathrm{P}$ quantum wells

InGaAs/InP strained-layer modulation-doped quantum wells were studied by photoluminescence. The combination of the built-in strain and the quantum confinement in this system leads to a strong valence band mixing yielding direct and indirect band gap structures. We demonstrate that the optical emission line shape is strongly dependent on the valence band dispersion and it is a good method to distinguish between direct and indirect structures. The application of an external biaxial tensile strain to the samples provides an additional evidence of direct-to-indirect band gap transition in strained heterostructures.