Magnetoreflectivity study of excitons in (Zn,Co)Se epilayers

The reflectivity spectra from single-crystal epilayers of the diluted magnetic semiconductor Zn1-x Cox Se(x=0.0076, x=0.0104) have been studied as functions of magnetic field and temperature. The excitonic spin splitting in these crystals saturates for magnetic fields B>5 T, indicating that (Zn,Co)Se is a Brillouin paramagnet, in agreement with magnetization and electron-paramagnetic-resonance studies on the same samples. The magnetoreflectivity data yield a value for the exchange parameter difference N0 (α-β)=2420±40 meV, significantly larger than the values obtained for either Fe- or Mn-based diluted magnetic semiconductors studied to date.