Cathodoluminescence Studies of Polytype Structure in Zn$\text{}_{1-x}$Mg$\text{}_{x}$Se

Zn$\text{}_{1-x}$Mg$\text{}_{x}$Se crystals grown by Bridgman method show spatial transition from sphalerite (3C) to wurzite structure (2H) with increasing Mg content (x). Within the transition range, near x=0.19, coexistence of hexagonal and cubic structure results in the formation of polytype sequences of 3C-8H-4H-2H. We have investigated the spatial distribution of the polytypes in Zn$\text{}_{1-x}$Mg$\text{}_{x}$Se mixed crystals with a value of x close to that of the phase transition using spectrally as well as spatially resolved cathodoluminescence. Three emission bands in the cathodoluminescence spectrum have been observed, two strong lines at 2.99 eV and 2.965 eV, and a weak shoulder at 2.95 eV. The lines at 2.965 and 2.99 eV are known in the literature as an exciton recombination in the 8H and 4H polytype structure. We have found the third one at 2.95 eV to be due to luminescence in the 3C structure. These results demonstrate the usefulness of cathodoluminescence measurements for investigations of spatial distribution of inhomogeneities of mixed semiconductors.