Temperature-dependent Raman scattering of natural and isotopically substituted PbS

Abstract

Lead sulfide is an important semiconductor that has found technological applications for over a century. Raman spectroscopy, a standard tool for the investigation and characterization of semiconductors, has limited application to this material because of the forbidden nature of its first order scattering and its opacity to visible lasers. Nevertheless, useful vibrational spectra from two-phonon processes are obtained with red lasers, probably because of a resonance in the concomitant electronic transitions. Herewith, we report temperature dependent Raman spectra covering the 10–300 K range, for two samples with different sulfur isotopic compositions. The results are analyzed by comparison with ab initio cal- culations of the lattice dynamics of PbS and the corresponding densities of one and two-phonon states. Emphasis is placed on the analysis of the two phonon band centered at ∼430 cm–1. The combined use of ab initio calculations and an extended temperature range (compared to previous reports) allows an unequivocal identification of some of the main features in the second-order Raman spectra. Our study also provides a much firmer background for the understanding of anomalous temperature dependences in the anharmonic shifts of second-order Raman spectra in PbS.