Reflectivity measurements were made to determine the variation with composition of the lowest gap $E_0$ together with its spin-orbit-split gap $E_0+{\Delta }_0$ in $\mathrm{Zn}{\mathrm{S}}_x{\mathrm{Se}}_{1-x}$ at room temperature. The variation of these gaps indicates that $\mathrm{Zn}{\mathrm{S}}_x{\mathrm{Se}}_{1-x}$ is an amalgamation-type alloy, at least for these gaps, contrary to a previous suggestion of a persistence type. The bowing parameters of the $E_0$ and $E_0+{\Delta }_0$ gaps are determined to be 0.630 ± 0.030 and 0.596 ± 0.023 eV, respectively. The variation with composition of the spin-orbit splitting ${\Delta }_0$ tends to be convex as in the case of $\mathrm{Zn}{\mathrm{Se}}_x{\mathrm{Te}}_{1-x}$ alloys. The negative bowing of ${\Delta }_0$ may be interpreted in terms of the virtual-crystal approximation.

• Received 20 March 1974

DOI:https://doi.org/10.1103/PhysRevB.10.2495