Raman and reflectivity spectra of cubic ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Se epilayers grown by molecular-beam epitaxy

We present a Raman-scattering, reflectivity, and photoluminescence study of ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$Se epilayers grown by molecular-beam expitaxy on (001) GaAs substrates. These epilayers exhibit the cubic (zinc-blende) structure, even though in bulk crystal growth this alloy crystallizes in the wurtzite form. The energy gap as a function of x is studied by reflectivity and photoluminescence. We also present a Raman study of the frequency of the zone-center optical phonons as a function of x, extending the previous work to higher values of x. The magnetic-field dependence of the spin-flip Raman shift of donor-bound electrons and of the free-excitonic photoluminescence shows the huge Zeeman shifts typically encountered in diluted magnetic semiconductors, allowing an estimate of the ratio between the conduction (α) and valence (β) -band exchange constants, ‖α/β${\mathrm{\Vert }}_{\mathrm{cubic}}$=0.80, a value somewhat larger than that in the wurtzite structure. We also investigate the Raman features associated with spin flip of donor-bound electrons in epilayers with large x, where the strong antiferromagnetic coupling comes into play. In addition, we report the anomalous behavior of photoluminescence peaks observed for high values of x, which we have attributed to deep impurity levels resulting in transition energies just above the 2.2-eV emission of ${\mathrm{Mn}}^{2+}$.