Optical properties of Zn _1-xMn _xTe epilayers grown by molecular beam epitaxy

Zn _1-xMn _xTe (0≤x≤0.268) epilayers were grown on GaAs(001) substrates by molecular beam epitaxy. The optical properties of the epilayers were studied using reflectivity, transmission, and photoluminescence (PL) measurements. The energy gaps of the epilayers were found to increase linearly with Mn concentration. From the PL spectra, a redshift of the PL peaks was observed as the temperature was increased. The exciton activation energies of the epilayers were determined by the plots of logarithmic-integrated PL intensity versus inverse temperature. Accordingly, they increase with Mn concentration. The Varshni and O'Donnell relations, which mimic the temperature dependence of semiconductor energy gaps were used to fit the experimental data [Y. P. Varshni, Physica 34, 149 (1967); R. P. O'Donnell and X. Chen, Appl. Phys. Lett. 58, 2924 (1991)]. Good fits were obtained by both relations. From the fitted results, the entropy of formation of electron-hole pairs in the Zn _1-xMn _xTe epilayers at room temperature was estimated to be roughly 0.5 meV/K.