Electroreflectance Measurements on ${\mathrm{Mg}}_2$Si, ${\mathrm{Mg}}_2$Ge, and ${\mathrm{Mg}}_2$Sn

The room-temperature electroreflectance spectra of the II-VI compounds ${\mathrm{Mg}}_2$Si, ${\mathrm{Mg}}_2$Ge, and ${\mathrm{Mg}}_2$Sn are reported in the energy region 1.5-4.5 eV. All measurements were performed using the electrolyte technique with a nonaqueous electrolyte. These materials crystallize with the antifluorite crystal structure and are small-band-gap semiconductors. In all of the materials, a large number of sharp peaks were observed; the spectra are interpreted in terms of the reflectivity spectra and existing energy-band calculations. Special mention should be made of a doublet observed (1.64-1.84 eV) in the spectrum of ${\mathrm{Mg}}_2$Ge. This doublet appears to be due to the spin-orbit splitting of the ${\Gamma }_{15}$ valence band.