Raman study of phonon modes and disorder effects in Pb1−xSrxSe alloys grown by molecular beam epitaxy

We report phonon modes and alloy disorder effects of ${\mathrm{Pb}}_{1-x}{\mathrm{Sr}}_x\mathrm{Se}$ alloys $(x⩽0.3)$ grown on ${\mathrm{BaF}}_2$ (111) substrates by Raman spectroscopy measurements. On the basis of phonon modes in binary PbSe and SrSe, first-, second-, and high-order Raman scattering phonon frequencies of ternary ${\mathrm{Pb}}_{1-x}{\mathrm{Sr}}_x\mathrm{Se}$ are observed, together with the deduction of the disorder activated modes due to the breakdown of the selection rule. The alloy disorder is found to play a more important role than the strain effect in ${\mathrm{Pb}}_{1-x}{\mathrm{Sr}}_x\mathrm{Se}$ , and has been further investigated by employing the special correlation model. The PbSe-like second-order features are also shown to broaden slightly and diminish in intensity with increasing Sr concentration, which has been attributed to a weak breakdown in the long-range order.