Optical characterization of rocksalt Pb1–xSnx Te alloys

The optical properties in terms of dielectric function epsilon(h omega) = epsilon(1)(h omega) + i epsilon(3)(h omega) of rocksalt Pb1-xSnxTe alloys (0 <= x <= 1) are investigated experimentally by spectroscopic ellipsometry and theoretically by first-principles electronic band structure calculation. We find a strong optical response in the 0.5-2.0 eV region arising from optical absorption around the LW-Iine of the Brillouin zone. The response peak of the imaginary part of the dielectric functions at E = 1.6-1.8 1.8 eV shifts towards lower energies for high Sn compositions as a consequence of narrower W-point band-gap E-g(W) for the Sn-rich alloys.