Optical properties of Zn_1-xMn_xSe (x≤0.78) epilayers

The optical properties of Zn_1-xMn_xSe with x up to 0.78 grown by molecular beam epitaxy on GaAs (001) substrates are reported. The complex dielectric functions ε=ε₁+iε₂ are obtained by spectroscopic ellipsometry in the photon range from 3.5 to 5.5 eV at room temperature. The critical-point energies E₁ and E₁+Δ₁ for x ≤ 0.52 are determined by fitting the calculated second-derivative spectra of ε to the standard line shape. For the sample with x = 0.78, the peak position in the ε₂ spectrum is taken as an estimate for E₁. While the fundamental band gap E₀ increases with x, the E₁ and E₁+Δ₁ energies decrease almost linearly with x. Comparing our results with those of the other experimental and theoretical studies, we consider the sp-d hybridization between the Mn 3d level and the sp band states to be an important factor affecting the band structures at the L point in the Brillouin zone over the whole range of Mn concentration.