Far Infrared to Visible Optical Study of PbSe, PbTe, and PbS

PbSe, PbTe, and PbS have attracted attention due to their interesting optical and electronic properties. In particular, much of the interest is concerned with the narrow band gap properties useful for optical devices and radiation detectors. To study the optical properties of atomic layer-deposited Pb-based chalcogenide thin films, we used three spectrometers, spanning a spectral range from far-IR to visible frequencies. Two of the instruments were spectroscopic Woollam ellipsometers with a combine range between 50000 cm^-1 and 250 cm^-1 . The other instrument was a Bruker VERTEX 80v FTIR that covered a spectral range between 8000 cm^-1 and 85 cm^-1 . Initially, the ellipsometry spectra were fitted using CompleteEASE software, where the dielectric functions were modeled as a collection of oscillators, each representing an electronic or phononic transition. Following the ellipsometry analysis, we extended the models to yield the reflectivity of samples, which were obtained by the FTIR spectrometer. The combined analysis, using both ellipsometry and FTIR, allows us to obtain the dielectric functions of PbSe, PbTe, and PbS in a wide spectral range. In addition, upon further analysis of their dielectric functions, we are able to gain insights on the electronic and phononic behavior of these materials.