On the onset of strain relaxation in the Al_0.45Ga_0.55As/In_xGa_1−xAs active region in quantum cascade laser structures

The Al_0.45Ga_0.55As/In_xGa_1−xAs active regions in quantum cascade laser structures grown on (001) GaAs substrates were investigated using the high-resolution X-ray diffraction method. The onset of the strain relaxation process has been studied. Reciprocal-space mapping showed that diffuse scattering is visible in the early stage of relaxation for the structure with x = 2.64% in the In_xGa_1−xAs layers. It has been proved that the diffuse scattering is the result of misfit dislocations generated by partial relaxation of the structures. The integration of the diffuse scattering has enabled determination of the dislocation density.