Optical-phonon behavior inZn1−xMnxSe: Zinc-blende and wurtzite structures

Optical phonons of mixed-crystal ${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$Se in both zinc-blende and wurtzite structures are investigated by Raman scattering. A calculation of the compositional dependence of the optical-phonon frequency in ${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$Se is performed using a modified random-element isodisplacement model with some detailed consideration. It confirms that ${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$Se shows an intermediate-mode behavior. The constant Θ which describes the effect of variation of the lattice parameter on the force constants should be different for individual mixed crystals. The phonon-mode splitting in wurtzite-structure ${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$Se is mainly attributed to the directional dependence of the force constants.