Visible-near ultraviolet ellipsometric study of Zn_1-xMg_xSe and Zn_1-xBe_xSe alloys

We report pseudodielectric function data 〈∈〉=〈∈₁〉+i〈∈ ₂〉 of Zn_1-xMg_xSe and Zn_1-xBe_xSe samples grown on GaAs substrates. The data were obtained from 1.5 to 6.0 eV using spectroscopic ellipsometry. Critical point parameters were obtained by fitting model line shapes to numerically calculated second energy derivatives of 〈∈〉, from which the bowing parameters and spin-orbit-splitting Δ₁ of the E₁ and E₁+Δ₁ gaps were obtained. A transfer of oscillator strength from E₁+Δ₁ to E₁ with increasing Mg and Be composition and a positive bowing of these threshold energies are attributed to the k-linear interaction, which is large in small-band gap semiconductors.