Dielectric functions and critical points of strained InxGa1−xAs on GaAs

Dielectric function spectra of strained InxGa1−xAs (x≤0.25) epilayers on GaAs are presented for the first time, together with spectra of relaxed layers of the same compositions. Critical point energies, obtained by line-shape fitting to second-derivative spectroscopic ellipsometry (SE) data, show an increase in the E1, E1+Δ1 splitting with strain, in agreement with theory using GaAs deformation potentials. SE is shown to be capable of determining layer thickness, composition, and strain in this alloy system.