Raman Spectroscopy of Multiphonon Emission Process in Ni-Doped PbTe

In this paper, we present room temperature unpolarized Raman scattering spectra of Ni doped PbTe single crystal sample. Crystal of PbTe(Ni) was grown by the Bridgman method. The Ni concentration in the sample used here was 1× $10^{19}$ at./$cm^{3}$. Well resolved peaks appear at about 126, 143, 181, 362 and 724 $cm^{-1}$. The modes at 126 and 143 $cm^{-1}$, which are also observed in other telluride compounds, originate from vibrations in $TeO_2$. We assume that the mode at about 181 $cm^{-1}$ is connected to excitations of a local phonon mode in the vicinity of an impurity atom (donor $Ni^{3+}$ state). Modes at about 362 $cm^{-1}$ and 724 $cm^{-1}$ are the second and fourth harmonic of a local phonon mode, registered here due to multiphonon emission.