Dielectric function and band structure of Sn1−xGex (x < 0.06) alloys on InSb

Abstract

Tin-rich Sn1−xGex alloys with Ge contents up to 6% were grown pseudomorphically on InSb (001) substrates by molecular beam epitaxy at room temperature. The alloys show a germanium-like lattice and electronic structure and respond to the biaxial stress within continuum elasticity theory, which influences bands and interband optical transitions. The dielectric function of these alloys was determined from 0.16 to 4.7 eV using Fourier-transform infrared and spectroscopic ellipsometry. The E1 and E1 + Δ1 critical points decrease with the increasing Ge content with a bowing parameter similar to the one established for Ge-rich Sn1−xGex alloys. On the other hand, the inverted direct bandgap E¯0 is nearly independent of the Ge content, which requires a bowing parameter of about 0.8 eV, much lower than what has been established using photoluminescence experiments of Ge-rich relaxed Sn1−xGex alloys.