Temperature dependence of the dielectric function and interband transitions of pseudomorphic GeSn alloys

The authors investigated the temperature dependence of the complex dielectric function and interband transitions of pseudomorphic Ge1-xSnx (x-0, 0.025, and 0.075) alloys using spectroscopic ellipsometry from 77 to 400K. The dielectric functions and interband transitions of the alloys blue-shift with decreasing temperature. The dependence of E-1, E-1 + Delta(1), and E-2 transitions on temperature can be represented by either Varshni's empirical formula or an expression proportional to the Bose-Einstein statistical factor of an average phonon. The authors find that the temperature-dependence is similar to that of bulk Ge with the exception of an offset accounting for the alloying of alpha-Sn into Ge. In addition, the temperature-dependent E-1 and E-1 + Delta(1) transition energies in pseudomorphic GeSn alloys can be predicted by combining their room-temperature compositional dependencies with the energy shifts resulting from the temperature dependence of these transitions in Ge. (C) 2016 American Vacuum Society.