Raman scattering in PbTe and PbSnTe films: In situ phase transformations

The PbTe and Pb$_{1-x}$Sn$_x$Te films, both undoped and doped with indium, are studied by Raman spectroscopy. It is found that the film surface changes during spectra recording. From comparative analysis of the data obtained in the study and those reported in publications, it is inferred that the 90, 117, and 138 cm$^{-1}$ peaks correspond to the scattering of light at tellurium or tellurium-oxide precipitates. It is established that these peaks appear in the spectra of Pb$_{1-x}$Sn$_x$Te films and epitaxial PbTe films only when doped with indium. The 180-cm$^{-1}$ peak is observed in the spectra of all of the samples and not attributed to the plasmon-phonon mode. The nature of the 180-cm$^{-1}$ peak is still not completely understood.