Raman-scattering study of the high-pressure phase transition inCd1−xMnxTe

The high-pressure phase transition in ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Mn}}_{\mathrm{x}}$Te from the cubic zinc-blende structure to the NaCl structure is investigated by Raman scattering. The measurements are made while increasing as well as decreasing the pressure. The transition pressure depends on composition and shows hysteresis. The behavior of zone-center optical phonons as well as that of zone-boundary acoustic phonons, which appear in the first-order Raman spectra due to the disorder in the mixed crystal, are investigated. The zone-boundary acoustic phonon TA(X) shows softening similar to that observed in other compound semiconductors. The longitudinal-optic (LO) phonon frequencies in pure CdTe observed while decreasing pressure match with those observed while increasing pressure whereas in the mixed crystals there is a marked difference. As a result of cycling through the phase transition, the CdTe-like LO-phonon frequencies measured at the ambient pressure are higher compared to those before the cycling; the MnTe-like LO-phonon frequencies show an opposite behavior. This change in the LO-TO splitting of the CdTe-like and MnTe-like modes implies a redistribution of the mode effective charges associated with these modes such that the net charge remains unchanged.