Temperature dependence of the dielectric function and the interband critical-point parameters of GaSb

We have used spectroscopic ellipsometry to measure the dielectric function ε(ω) of GaSb from 10 to 740 K in the 1.4–5.6 eV photon-energy region. By performing a line-shape analysis of the observed structures, the interband critical-point parameters (strength, threshold energy, broadening, and excitonic phase angle) and their temperature dependence have been determined. The observed decrease in energy after correction for the effect of thermal expansion and the corresponding increase in broadening with increasing temperature agree well with the results of a calculation that takes into account the Debye-Waller and self-energy terms of the deformation-potential-type electron-phonon interaction.