Raman-line-shape study ofInxGa1−xAs on InP and GaAs substrates

Raman scattering of ${\mathrm{In}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As epitaxial layers on InP and GaAs substrates have been investigated with a wide range of composition. It is found that the asymmetric broadening of LO phonon modes varies with composition as well as substrate. With the spatial correlation model, the Raman line shapes of the GaAs-like mode in ${\mathrm{In}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As epitaxial layers have been analyzed. It is found that the one-parameter spatial correlation model cannot explain the experimental results. According to the measurements of double-crystal x-ray diffraction (DXRD), we find strong correlation between the full width at half maximum of DXRD measurements and the line shapes of the Raman spectra. Thus, it is suggested that the Raman line shapes depend not only on the alloy disorder but also on the degree of structural dislocation in the heteroepitaxial system. Structural dislocation will change the intrinsic linewidth of the Raman spectrum which introduces an additional fitting parameter in the spatial-correlation model. Thus, our results provide a framework for the use of the two-parameter spatial-correlation model in the study of the compositional dependence of the Raman spectra in epilayer structures.