Visible-near ultraviolet ellipsometric study of $Zn1−xMgxSe$ and $Zn1−xBexSe$ alloys

We report pseudodielectric function data $〈ε〉=〈ε1〉+i〈ε2〉$ of $Zn1−xMgxSe$ and $Zn1−xBexSe$ 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 $〈ε〉,$ 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.