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

Abstract

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 400 K. The dielectric functions and interband transitions of the alloys blue-shift with decreasing temperature. The dependence of E1, E1 + Δ1, and E2 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 α-Sn into Ge. In addition, the temperature-dependent E1 and E1 + Δ1 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.