DEFECT AND STRAIN REDISTRIBUTION IN INXGA1-XAS/GAAS MULTIPLE-QUANTUM WELLS STUDIED BY RESONANT RAMAN-SCATTERING

Resonant Raman scattering by longitudinal optical (LO) phonons in the GaAs barriers of InxGa1-xAs/GaAs multiple quantum well structures has been used to study the onset of strain relaxation as the number of quantum wells is increased. The intensity of scattering from one and two GaAs LO phonons for excitation in resonance with the GaAs E0 + DELTA0 band gap is found to be highly sensitive to the formation and/or redistribution of defects and the buildup of strain in the barriers, and thus to strain relaxation in the InxGa1-xAs quantum wells. This behavior allows us to detect the onset of strain redistribution, even in samples where the frequencies of both the GaAs LO phonon in the barrier layers and the GaAs-like LO phonon in the InxGa1-xAs quantum wells show no measurable shift. Here, the GaAs LO phonon frequency observed in structures with fully strained InxGa1-xAs wells and unstrained GaAs barriers is used as a reference.