Complex dielectric function of GaAs1-xBix as a function of Bi content

The complex dielectric constants of GaAs1-xBix alloys grown by molecular beam epitaxy with x=0% to 17% have been measured over the spectral range from 0.37 to 9.1 eV using spectroscopic ellipsometry. Critical points in the joint density of states have been analyzed by fitting the line shape of the Van Hove singularities in the dielectric function derived from the ellipsometry data. The critical points generally match similar critical points in the dielectric function of GaAs with at least one alternative critical point. The energy of the critical points involving transitions from the top of the valence band show a strong dependence on Bi concentration similar to the composition dependence of the band gap, while the other critical points have a weaker dependence on Bi concentration. The measured composition dependence of the band gap and the energy of the split-off hole band are in good agreement with density functional calculations. The composition dependence of the index of refraction in the vicinity of the band gap for GaAs1-xBix alloys is an order of magnitude larger than the composition dependence of the index of refraction in Ga1-xInxAs alloys.