MnSe: Rocksalt versus zinc-blende structure

Abstract

MnSe epilayers are grown on (001) GaAs substrates by molecular beam epitaxy (MBE), which exhibit NaCl structure as shown by x-ray diffraction. Their zone-center transverse optic (TO) and longitudinal optic (LO) phonons have been observed as minima in infrared transmission with oblique incidence, i.e., in the Berreman geometry, using Fourier transform infrared spectroscopy. In contrast, they are absent in the Raman spectrum, consistent with the rule of mutual exclusion. The TO and LO frequencies thus deduced, 139 and 239cm−1, respectively, differ significantly from the corresponding values of 219.5 and 257cm−1 obtained for zinc-blende MnSe. The latter were deduced from the →x1 values of the TO and LO frequencies from a Raman study of MBE-grown Cd1−xMnxSe epilayers. A similar study of ZnTe/MnSe multiple quantum well structure also yielded the LO at 249cm−1, compatible with the zinc-blende character of MnSe in such structures, combined with the strain experienced by them.