Optical study of ZnSe_xTe_{1 - X} alloys using spectroscopic ellipsometry

We report pseudodielectric function data 〈∈〉 = 〈∈₁〉 + i〈∈₂〉 of ZnSe_xTe_{1 - x} samples grown on GaAs substrates. The data were obtained from 1.5 to 6.5 eV using spectroscopic ellipsometry. Critical-point parameters were obtained by fitting model line shapes to numerically calculated second-energy derivatives of 〈∈〉. The bowing parameters of E₀, E₁, and E₁ + Δ₁ were determined and were comparable to that of E₀ quoted from the literature. We observed a monotonie increase of the linewidth of the E₁ gap up to x = 0.85, whereas that of E₁ + Δ₁ showed a maximum value near x = 0.5. We attribute this anomalous broadening of the E₁ gap to sample microstructures developed in the low-Te composition alloys.