Electron Effective Mass in PbS Single Crystals by Infrared Reflectivity Measurements

Abstract

Infrared reflectivity measurements have been performed on a series of PbS single crystals. The temperature dependence of conductivity effective mass m_s has been evaluated and used to compute the free‐carrier mobilities. Results show how m_s decreases as the crystal temperature decreases. Further results show how m_s decreases as the carrier concentration decreases. The influence of crystal preparation on reflectivity properties has been studied. It has been determined that lead precipitates up to 10¹⁹ atoms/cm³ do not affect the minimum of the reflectivity curve but the homogeneity of the crystals does have a significant effect. Our determinations of conductivity effective mass of free carriers at each temperature have been used to compute the mobilities according to the two alternative theories of thermal vibration scattering, namely by acoustical and optical modes. Results show that the acoustical theory may not be used to predict temperature dependence of the mobilities, but that the optical polaron theory does give good predictions.