Optical properties of PbS

Spectroscopic ellipsometry has been used to measure the complex dielectric function epsilon(E) = epsilon(1)(E) + i epsilon(2)(E) of PbS single crystals. The measurements are made on cleaved PbS surfaces in the 1.5-5.3 eV photon-energy range at room temperature. It is found that the optical properties of PbS are very sensitive to air exposure. The observed epsilon(E) spectra reveal distinct structures at energies of the E-1, E-2, and E-3 critical points (CPs). These data and the literature values are used for the modeling of the optical constants of PbS over the 0.3-5.3 eV photon-energy range, including the band-gap (E-0 similar to 0.4 eV) region. It is shown that the three-dimensional M-0 CP (E-0) and damped harmonic-oscillator model (E-1, E-2, and E-3) provide satisfactory fits to the experimental optical-constant data. (C) 1998 American Institute of Physics. [S0021-8979(98)05411-5].